<FacebookShareButton url={url} quote={postNode.title}>
          <FacebookIcon round size={iconSize} />
          <FacebookShareCount url={url}>
            {count => <div className="share-count">{filter(count)}</div>}
          </FacebookShareCount>

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 98.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

        <RedditShareButton url={url} title={post.title}>
          <RedditIcon round size={iconSize} />
          <RedditShareCount url={url}>
            {count => <div className="share-count">{filter(count)}</div>}
          </RedditShareCount>

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 98.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

            <MainHeader className="post-head" cover={cover}>
              <MainNav>
                <BlogLogo logo={config.siteLogo} title={config.siteTitle} />
                <MenuButton
                  navigation={config.siteNavigation}

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 97.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

            <MainHeader className="author-head" cover={cover}>
              <MainNav>
                <BlogLogo logo={config.siteLogo} title={config.siteTitle} />
                <MenuButton
                  navigation={config.siteNavigation}

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 97.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

              <PaginatedContent
                page={page}
                pages={pages}
                total={total}
                limit={limit}

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 86.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

              <PaginatedContent
                page={page}
                pages={pages}
                total={total}
                limit={limit}

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 86.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

class AuthorProfile extends React.Component {
  render() {
    const { children, className } = this.props;
    const classes = classNames("author-profile", className);

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 77.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

class AuthorMeta extends React.Component {
  render() {
    const { children, className } = this.props;
    const classes = classNames("author-meta", className);

Close

Duplicated Code

Duplicated code can lead to software that is hard to understand and difficult to change. The Don't Repeat Yourself (DRY) principle states:

Every piece of knowledge must have a single, unambiguous, authoritative representation within a system.

When you violate DRY, bugs and maintenance problems are sure to follow. Duplicated code has a tendency to both continue to replicate and also to diverge (leaving bugs as two similar implementations differ in subtle ways).

Tuning

This issue has a mass of 77.

We set useful threshold defaults for the languages we support but you may want to adjust these settings based on your project guidelines.

The threshold configuration represents the minimum mass a code block must have to be analyzed for duplication. The lower the threshold, the more fine-grained the comparison.

If the engine is too easily reporting duplication, try raising the threshold. If you suspect that the engine isn't catching enough duplication, try lowering the threshold. The best setting tends to differ from language to language.

See codeclimate-duplication's documentation for more information about tuning the mass threshold in your .codeclimate.yml.

Refactorings

• Extract Method
• Extract Class
• Form Template Method
• Introduce Null Object
• Pull Up Method
• Pull Up Field
• Substitute Algorithm

Further Reading

• Don't Repeat Yourself on the C2 Wiki
• Duplicated Code on SourceMaking
• Refactoring: Improving the Design of Existing Code by Martin Fowler. Duplicated Code, p76

const mapToListParts = (item, index) => {
  if (typeof item === "string" || typeof item === "number") {
    return createElement(ListItem, { key: item, primaryText: item });
  }
  if (isValidElement(item)) {

Close

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

  getLocalTitle() {
    function capitalize(string) {
      return string.charAt(0).toUpperCase() + string.slice(1);
    }
    const pathPrefix = config.pathPrefix ? config.pathPrefix : "/";

Close

Cognitive Complexity

Cognitive Complexity is a measure of how difficult a unit of code is to intuitively understand. Unlike Cyclomatic Complexity, which determines how difficult your code will be to test, Cognitive Complexity tells you how difficult your code will be to read and comprehend.

A method's cognitive complexity is based on a few simple rules:

• Code is not considered more complex when it uses shorthand that the language provides for collapsing multiple statements into one
• Code is considered more complex for each "break in the linear flow of the code"
• Code is considered more complex when "flow breaking structures are nested"

Further reading

• Cognitive Complexity docs
• Cognitive Complexity: A new way of measuring understandability

.gist td {

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

input { line-height: normal; }

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

.gist td {

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

hr {

Close

no-duplicate-selectors

Disallow duplicate selectors within a stylesheet.

<!-- prettier-ignore -->

.foo {} .bar {} .foo {}
/** ↑              ↑
 * These duplicates */

This rule checks for two types of duplication:

• Duplication of a single selector with a rule's selector list, e.g. a, b, a {}.
• Duplication of a selector list within a stylesheet, e.g. a, b {} a, b {}. Duplicates are found even if the selectors come in different orders or have different spacing, e.g. a d, b > c {} b>c, a d {}.

The same selector is allowed to repeat in the following circumstances:

• It is used in different selector lists, e.g. a {} a, b {}.
• The duplicates are determined to originate in different stylesheets, e.g. you have concatenated or compiled files in a way that produces sourcemaps for PostCSS to read, e.g. postcss-import.
• The duplicates are in rules with different parent nodes, e.g. inside and outside of a media query.

This rule resolves nested selectors. So a b {} a { & b {} } counts as a violation, because the resolved selectors end up with a duplicate.

blockquote cite a { font-weight: normal; }

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

blockquote cite a { font-weight: normal; }

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

body {

Close

no-duplicate-selectors

Disallow duplicate selectors within a stylesheet.

<!-- prettier-ignore -->

.foo {} .bar {} .foo {}
/** ↑              ↑
 * These duplicates */

This rule checks for two types of duplication:

• Duplication of a single selector with a rule's selector list, e.g. a, b, a {}.
• Duplication of a selector list within a stylesheet, e.g. a, b {} a, b {}. Duplicates are found even if the selectors come in different orders or have different spacing, e.g. a d, b > c {} b>c, a d {}.

The same selector is allowed to repeat in the following circumstances:

• It is used in different selector lists, e.g. a {} a, b {}.
• The duplicates are determined to originate in different stylesheets, e.g. you have concatenated or compiled files in a way that produces sourcemaps for PostCSS to read, e.g. postcss-import.
• The duplicates are in rules with different parent nodes, e.g. inside and outside of a media query.

This rule resolves nested selectors. So a b {} a { & b {} } counts as a violation, because the resolved selectors end up with a duplicate.

blockquote p {

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

table tbody > tr:nth-child(odd) > td,

Close

no-descending-specificity

Disallow selectors of lower specificity from coming after overriding selectors of higher specificity.

<!-- prettier-ignore -->

#container a { top: 10px; } a { top: 0; }
/** ↑                           ↑
 * The order of these selectors represents descending specificity */

Source order is important in CSS, and when two selectors have the same specificity, the one that occurs last will take priority. However, the situation is different when one of the selectors has a higher specificity. In that case, source order does not matter: the selector with higher specificity will win out even if it comes first.

The clashes of these two mechanisms for prioritization, source order and specificity, can cause some confusion when reading stylesheets. If a selector with higher specificity comes before the selector it overrides, we have to think harder to understand it, because it violates the source order expectation. Stylesheets are most legible when overriding selectors always come after the selectors they override. That way both mechanisms, source order and specificity, work together nicely.

This rule enforces that practice as best it can, reporting fewer errors than it should. It cannot catch every actual overriding selector, but it can catch certain common mistakes.

How it works

This rule looks at the last compound selector in every full selector, and then compares it with other selectors in the stylesheet that end in the same way.

So .foo .bar (whose last compound selector is .bar) will be compared to .bar and #baz .bar, but not to #baz .foo or .bar .foo.

And a > li#wag.pit (whose last compound selector is li#wag.pit) will be compared to div li#wag.pit and a > b > li + li#wag.pit, but not to li or li #wag, etc.

Selectors targeting pseudo-elements are not considered comparable to similar selectors without the pseudo-element, because they target other elements on the rendered page. For example, a::before {} will not be compared to a:hover {}, because a::before targets a pseudo-element whereas a:hover targets the actual <a>.

This rule only compares rules that are within the same media context. So a {} @media print { #baz a {} } is fine.

This rule resolves nested selectors before calculating the specificity of the selectors.

DOM Limitations

The linter can only check the CSS to check for specificity order. It does not have access to the HTML or DOM in order to interpret the use of the CSS.

This can lead to valid linting errors appearing to be invalid at first glance.

For example the following will cause an error:

<!-- prettier-ignore -->

.component1 a {}
.component1 a:hover {}
.component2 a {}

This is a correct error because the a:hover on line 2 has a higher specificity than the a on line 3.

This may lead to confusion because "the two selectors will never match the same a in the DOM". However, since the linter does not have access to the DOM it can not evaluate this, and therefore correctly reports the error about descending specificity.

It may be possible to restructure your CSS to remove the error, otherwise it is recommended that you disable the rule for that line and leave a comment saying why the error should be ignored. Note that disabling the rule will cause additional valid errors from being reported.

table {

Close

no-duplicate-selectors

Disallow duplicate selectors within a stylesheet.

<!-- prettier-ignore -->

.foo {} .bar {} .foo {}
/** ↑              ↑
 * These duplicates */

This rule checks for two types of duplication:

• Duplication of a single selector with a rule's selector list, e.g. a, b, a {}.
• Duplication of a selector list within a stylesheet, e.g. a, b {} a, b {}. Duplicates are found even if the selectors come in different orders or have different spacing, e.g. a d, b > c {} b>c, a d {}.

The same selector is allowed to repeat in the following circumstances:

• It is used in different selector lists, e.g. a {} a, b {}.
• The duplicates are determined to originate in different stylesheets, e.g. you have concatenated or compiled files in a way that produces sourcemaps for PostCSS to read, e.g. postcss-import.
• The duplicates are in rules with different parent nodes, e.g. inside and outside of a media query.

This rule resolves nested selectors. So a b {} a { & b {} } counts as a violation, because the resolved selectors end up with a duplicate.