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eb39fafa4f
includes a (minimal) working wrapper Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
132 lines
3.0 KiB
Markdown
132 lines
3.0 KiB
Markdown
# require or disallow initialization in variable declarations (init-declarations)
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In JavaScript, variables can be assigned during declaration, or at any point afterwards using an assignment statement. For example, in the following code, `foo` is initialized during declaration, while `bar` is initialized later.
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```js
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var foo = 1;
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var bar;
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if (foo) {
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bar = 1;
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} else {
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bar = 2;
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}
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```
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## Rule Details
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This rule is aimed at enforcing or eliminating variable initializations during declaration. For example, in the following code, `foo` is initialized during declaration, while `bar` is not.
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```js
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var foo = 1;
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var bar;
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bar = 2;
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```
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This rule aims to bring consistency to variable initializations and declarations.
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## Options
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The rule takes two options:
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1. A string which must be either `"always"` (the default), to enforce initialization at declaration, or `"never"` to disallow initialization during declaration. This rule applies to `var`, `let`, and `const` variables, however `"never"` is ignored for `const` variables, as unassigned `const`s generate a parse error.
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2. An object that further controls the behavior of this rule. Currently, the only available parameter is `ignoreForLoopInit`, which indicates if initialization at declaration is allowed in `for` loops when `"never"` is set, since it is a very typical use case.
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You can configure the rule as follows:
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Variables must be initialized at declaration (default)
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```json
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{
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"init-declarations": ["error", "always"],
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}
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```
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Variables must not be initialized at declaration
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```json
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{
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"init-declarations": ["error", "never"]
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}
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```
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Variables must not be initialized at declaration, except in for loops, where it is allowed
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```json
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{
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"init-declarations": ["error", "never", { "ignoreForLoopInit": true }]
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}
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```
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### always
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Examples of **incorrect** code for the default `"always"` option:
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```js
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/*eslint init-declarations: ["error", "always"]*/
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/*eslint-env es6*/
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function foo() {
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var bar;
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let baz;
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}
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```
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Examples of **correct** code for the default `"always"` option:
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```js
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/*eslint init-declarations: ["error", "always"]*/
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/*eslint-env es6*/
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function foo() {
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var bar = 1;
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let baz = 2;
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const qux = 3;
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}
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```
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### never
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Examples of **incorrect** code for the `"never"` option:
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```js
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/*eslint init-declarations: ["error", "never"]*/
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/*eslint-env es6*/
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function foo() {
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var bar = 1;
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let baz = 2;
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for (var i = 0; i < 1; i++) {}
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}
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```
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Examples of **correct** code for the `"never"` option:
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```js
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/*eslint init-declarations: ["error", "never"]*/
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/*eslint-env es6*/
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function foo() {
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var bar;
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let baz;
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const buzz = 1;
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}
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```
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The `"never"` option ignores `const` variable initializations.
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### ignoreForLoopInit
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Examples of **correct** code for the `"never", { "ignoreForLoopInit": true }` options:
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```js
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/*eslint init-declarations: ["error", "never", { "ignoreForLoopInit": true }]*/
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for (var i = 0; i < 1; i++) {}
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```
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## When Not To Use It
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When you are indifferent as to how your variables are initialized.
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