eslint/no-multi-assign Style

What it does

Disallow use of chained assignment expressions.

Why is this bad?

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.

Examples

Examples of incorrect code for this rule:

var a = (b = c = 5);

const foo = (bar = "baz");

let d = (e = f);

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

a = b = "quux";

Examples of correct code for this rule:

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

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

let d = c;
let e = 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:

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:

let a = (b = "baz");

const foo = (bar = 1);

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

References

• Rule Source