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content/snippets/react/s/lifecycle-hooks.md

Summary

Maintainability
Test Coverage

Line length
Open

For the `componentDidMount` lifecycle method, you can use the `useEffect()` hook with an empty array as the second argument. This will execute the provided callback only once when the **component is mounted**.

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.

Line length
Open

excerpt: If you're transitioning from class components to functional components, you can replicate the behavior of lifecycle methods using hooks.

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.

Line length
Open

Finally, for the `componentWillUnmount` lifecycle method, you can use the `useEffect()` hook with an empty array as the second argument. Return the provided callback to be executed only once **before cleanup**.

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.

First header should be a top level header
Open

## `useComponentDidMount` hook

MD002 - First header should be a top level header

Tags: headers

Aliases: first-header-h1

Parameters: level (number; default 1)

This rule is triggered when the first header in the document isn't a h1 header:

## This isn't a H1 header

### Another header

The first header in the document should be a h1 header:

# Start with a H1 header

## Then use a H2 for subsections

Line length
Open

If you're transitioning from **class components** to functional components, you might find yourself in need of replicating the behavior of **lifecycle methods**. Luckily, hooks can take care of that for you.

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.

Line length
Open

In order to replicate the behavior of `componentDidUpdate`, you can use the `useRef()` hook to create a variable, `mounted`, that tracks if the component has been mounted. Then, use the `useEffect()` hook to set the value of `mounted` to `true` the first time the hook is executed. Run the provided `callback` on subsequent hook executions.

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.

Line length
Open

For the `componentDidUpdate` lifecycle method, you can use the `useEffect()` hook with a condition as the second argument. This will execute the provided callback **every time** the condition changes.

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.

Line length
Open

Providing a dependency array for the second argument, `condition`, will only execute the hook if any of the dependencies change.

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.

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