Versions

no-multi-assign

Disallow use of chained assignment expressions

Chaining the assignment of variables can lead to unexpected results and be difficult to read.

(function() {
const foo = bar = 0; // Did you mean `foo = bar == 0`?
bar = 1; // This will not fail since `bar` is not constant.
})();
console.log(bar); // This will output 1 since `bar` is not scoped.

Rule Details

This rule disallows using multiple assignments within a single statement.

Examples of incorrect code for this rule:

/*eslint no-multi-assign: "error"*/

var a = b = c = 5;

const foo = bar = "baz";

let a =
b =
c;

class Foo {
a = b = 10;
}

a = b = "quux";

Examples of correct code for this rule:

/*eslint no-multi-assign: "error"*/

var a = 5;
var b = 5;
var c = 5;

const foo = "baz";
const bar = "baz";

let a = c;
let b = c;

class Foo {
a = 10;
b = 10;
}

a = "quux";
b = "quux";

Options

This rule has an object option:

  • "ignoreNonDeclaration": When set to true, the rule allows chains that don’t include initializing a variable in a declaration or initializing a class field. Default is false.

ignoreNonDeclaration

Examples of correct code for the { "ignoreNonDeclaration": true } option:

/*eslint no-multi-assign: ["error", { "ignoreNonDeclaration": true }]*/

let a;
let b;
a = b = "baz";

const x = {};
const y = {};
x.one = y.one = 1;

Examples of incorrect code for the { "ignoreNonDeclaration": true } option:

/*eslint no-multi-assign: ["error", { "ignoreNonDeclaration": true }]*/

let a = b = "baz";

const foo = bar = 1;

class Foo {
a = b = 10;
}

Version

This rule was introduced in ESLint v3.14.0.

Resources