Require Guarding for-in (guard-for-in)

Looping over objects with a for in loop will include properties that are inherited through the prototype chain. This behavior can lead to unexpected items in your for loop.

for (key in foo) {
    doSomething(key);
}

Note that simply checking foo.hasOwnProperty(key) is likely to cause an error in some cases; see [no-prototype-builtins](no-prototype-builtins.md).

Rule Details

This rule is aimed at preventing unexpected behavior that could arise from using a for in loop without filtering the results in the loop. As such, it will warn when for in loops do not filter their results with an if statement.

Examples of incorrect code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    doSomething(key);
}

Examples of correct code for this rule:

/*eslint guard-for-in: "error"*/

for (key in foo) {
    if (Object.prototype.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
    if ({}.hasOwnProperty.call(foo, key)) {
        doSomething(key);
    }
}

Related Rules

• [no-prototype-builtins](no-prototype-builtins.md)

Further Reading

• Exploring JavaScript for-in loops
• The pitfalls of using objects as maps in JavaScript Source: http://eslint.org/docs/rules/

MD034 - Bare URL used

Tags: links, url

Aliases: no-bare-urls

This rule is triggered whenever a URL is given that isn't surrounded by angle brackets:

For more information, see http://www.example.com/.

To fix this, add angle brackets around the URL:

For more information, see <http:></http:>.

Rationale: Without angle brackets, the URL isn't converted into a link in many markdown parsers.

Note: if you do want a bare URL without it being converted into a link, enclose it in a code block, otherwise in some markdown parsers it will be converted:

`http://www.example.com`

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD034 - Bare URL used

Tags: links, url

Aliases: no-bare-urls

This rule is triggered whenever a URL is given that isn't surrounded by angle brackets:

For more information, see http://www.example.com/.

To fix this, add angle brackets around the URL:

For more information, see <http:></http:>.

Rationale: Without angle brackets, the URL isn't converted into a link in many markdown parsers.

Note: if you do want a bare URL without it being converted into a link, enclose it in a code block, otherwise in some markdown parsers it will be converted:

`http://www.example.com`

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD004 - Unordered list style

Tags: bullet, ul

Aliases: ul-style

Parameters: style ("consistent", "asterisk", "plus", "dash"; default "consistent")

This rule is triggered when the symbols used in the document for unordered list items do not match the configured unordered list style:

* Item 1
+ Item 2
- Item 3

To fix this issue, use the configured style for list items throughout the document:

* Item 1
* Item 2
* Item 3

Note: the configured list style can be a specific symbol to use (asterisk, plus, dash), or simply require that the usage be consistent within the document.

MD022 - Headers should be surrounded by blank lines

Tags: headers, blank_lines

Aliases: blanks-around-headers

This rule is triggered when headers (any style) are either not preceded or not followed by a blank line:

# Header 1
Some text

Some more text
## Header 2

To fix this, ensure that all headers have a blank line both before and after (except where the header is at the beginning or end of the document):

# Header 1

Some text

Some more text

## Header 2

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse headers that don't have a blank line before, and will parse them as regular text.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD022 - Headers should be surrounded by blank lines

Tags: headers, blank_lines

Aliases: blanks-around-headers

This rule is triggered when headers (any style) are either not preceded or not followed by a blank line:

# Header 1
Some text

Some more text
## Header 2

To fix this, ensure that all headers have a blank line both before and after (except where the header is at the beginning or end of the document):

# Header 1

Some text

Some more text

## Header 2

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse headers that don't have a blank line before, and will parse them as regular text.

MD022 - Headers should be surrounded by blank lines

Tags: headers, blank_lines

Aliases: blanks-around-headers

This rule is triggered when headers (any style) are either not preceded or not followed by a blank line:

# Header 1
Some text

Some more text
## Header 2

To fix this, ensure that all headers have a blank line both before and after (except where the header is at the beginning or end of the document):

# Header 1

Some text

Some more text

## Header 2

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will not parse headers that don't have a blank line before, and will parse them as regular text.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

MD013 - Line length

Tags: line_length

Aliases: line-length Parameters: linelength, codeblocks, tables (number; default 80, boolean; default true)

This rule is triggered when there are lines that are longer than the configured line length (default: 80 characters). To fix this, split the line up into multiple lines.

This rule has an exception where there is no whitespace beyond the configured line length. This allows you to still include items such as long URLs without being forced to break them in the middle.

You also have the option to exclude this rule for code blocks and tables. To do this, set the code_blocks and/or tables parameters to false.

Code blocks are included in this rule by default since it is often a requirement for document readability, and tentatively compatible with code rules. Still, some languages do not lend themselves to short lines.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.

MD029 - Ordered list item prefix

Tags: ol

Aliases: ol-prefix

Parameters: style ("one", "ordered"; default "one")

This rule is triggered on ordered lists that do not either start with '1.' or do not have a prefix that increases in numerical order (depending on the configured style, which defaults to 'one').

Example valid list if the style is configured as 'one':

1. Do this.
1. Do that.
1. Done.

Example valid list if the style is configured as 'ordered':

1. Do this.
2. Do that.
3. Done.