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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
141 lines
3.5 KiB
Markdown
141 lines
3.5 KiB
Markdown
# Enforce spacing between rest and spread operators and their expressions (rest-spread-spacing)
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ES2015 introduced the rest and spread operators, which expand an iterable structure into its individual parts. Some examples of their usage are as follows:
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```js
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let numArr = [1, 2, 3];
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function add(a, b, c) {
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return a + b + c;
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}
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add(...numArr); // -> 6
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let arr1 = [1, 2, 3];
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let arr2 = [4, 5, 6];
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arr1.push(...arr2); // -> [1, 2, 3, 4, 5, 6]
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let [a, b, ...arr] = [1, 2, 3, 4, 5];
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a; // -> 1
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b // -> 2
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arr; // -> [3, 4, 5]
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function numArgs(...args) {
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return args.length;
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}
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numArgs(a, b, c); // -> 3
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```
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In addition to the above, there is currently a proposal to add object rest and spread properties to the spec. They can be used as follows:
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```js
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let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
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x; // -> 1
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y; // -> 2
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z; // -> { a: 3, b: 4 }
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let n = { x, y, ...z };
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n; // -> { x: 1, y: 2, a: 3, b: 4 }
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```
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As with other operators, whitespace is allowed between the rest or spread operator and the expression it is operating on, which can lead to inconsistent spacing within a codebase.
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## Rule Details
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This rule aims to enforce consistent spacing between rest and spread operators and their expressions. The rule also supports object rest and spread properties in ES2018:
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```json
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{
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"parserOptions": {
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"ecmaVersion": 2018
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}
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}
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```
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Please read the user guide's section on [configuring parser options](/docs/user-guide/configuring#specifying-parser-options) to learn more.
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## Options
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This rule takes one option: a string with the value of `"never"` or `"always"`. The default value is `"never"`.
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### "never"
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When using the default `"never"` option, whitespace is not allowed between spread operators and their expressions.
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```json
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rest-spread-spacing: ["error"]
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```
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or
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```json
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rest-spread-spacing: ["error", "never"]
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```
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Examples of **incorrect** code for this rule with `"never"`:
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```js
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/*eslint rest-spread-spacing: ["error", "never"]*/
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fn(... args)
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[... arr, 4, 5, 6]
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let [a, b, ... arr] = [1, 2, 3, 4, 5];
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function fn(... args) { console.log(args); }
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let { x, y, ... z } = { x: 1, y: 2, a: 3, b: 4 };
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let n = { x, y, ... z };
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```
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Examples of **correct** code for this rule with `"never"`:
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```js
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/*eslint rest-spread-spacing: ["error", "never"]*/
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fn(...args)
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[...arr, 4, 5, 6]
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let [a, b, ...arr] = [1, 2, 3, 4, 5];
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function fn(...args) { console.log(args); }
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let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
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let n = { x, y, ...z };
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```
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### "always"
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When using the `"always"` option, whitespace is required between spread operators and their expressions.
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```json
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rest-spread-spacing: ["error", "always"]
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```
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Examples of **incorrect** code for this rule with `"always"`:
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```js
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/*eslint rest-spread-spacing:["error", "always"]*/
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fn(...args)
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[...arr, 4, 5, 6]
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let [a, b, ...arr] = [1, 2, 3, 4, 5];
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function fn(...args) { console.log(args); }
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let { x, y, ...z } = { x: 1, y: 2, a: 3, b: 4 };
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let n = { x, y, ...z };
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```
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Examples of **correct** code for this rule with `"always"`:
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```js
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/*eslint rest-spread-spacing: ["error", "always"]*/
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fn(... args)
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[... arr, 4, 5, 6]
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let [a, b, ... arr] = [1, 2, 3, 4, 5];
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function fn(... args) { console.log(args); }
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let { x, y, ... z } = { x: 1, y: 2, a: 3, b: 4 };
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let n = { x, y, ... z };
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```
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## When Not To Use It
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You can safely disable this rule if you do not care about enforcing consistent spacing between spread operators and their expressions.
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## Further Reading
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* [Object Rest/Spread Properties for ECMAScript](https://github.com/tc39/proposal-object-rest-spread)
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