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eslint/init-declarations Style

What it does

Require or disallow initialization in variable declarations.

Why is this bad?

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.

var foo = 1;
var bar;
if (foo) {
  bar = 1;
} else {
  bar = 2;
}

Examples

Examples of incorrect code for the default "always" option:

/* init-declarations: ["error", "always"] */
function foo() {
  var bar;
  let baz;
}

Examples of incorrect code for the "never" option:

/* init-declarations: ["error", "never"] */
function foo() {
  var bar = 1;
  let baz = 2;
  for (var i = 0; i < 1; i++) {}
}

Examples of correct code for the default "always" option:

/* init-declarations: ["error", "always"] */

function foo() {
  var bar = 1;
  let baz = 2;
  const qux = 3;
}

Examples of correct code for the "never" option:

/* init-declarations: ["error", "never"] */

function foo() {
  var bar;
  let baz;
  const buzz = 1;
}

Examples of correct code for the "never", { "ignoreForLoopInit": true } options:

/* init-declarations: ["error", "never", { "ignoreForLoopInit": true }] */
for (var i = 0; i < 1; i++) {}

Configuration

The 1st option

type: "always" | "never"

"always"

Requires that variables be initialized on declaration. This is the default behavior.

"never"

Disallows initialization during declaration.

The 2nd option

This option is an object with the following properties:

ignoreForLoopInit

type: boolean

default: false

When set to true, allows uninitialized variables in the init expression of for, for-in, and for-of loops. Only applies when mode is set to "never".

How to use

To enable this rule using the config file or in the CLI, you can use:

Config (.oxlintrc.json)

{
  "rules": {
    "init-declarations": "error"
  }
}

CLI

oxlint --deny init-declarations

References

• Rule Source