no-multi-assign

In const width = height = 100, only width is declared. height is a plain assignment. It throws in strict mode if nothing declares it, and creates a global variable otherwise. Even when every name is declared, the second assignment is easy to overlook.

Configure

Off by default. To turn it on:

[lint.rules]
"no-multi-assign" = "error" # or "warn"

Every option, set to its default:

[lint.rules]
"no-multi-assign" = ["error", {
  ignoreNonDeclaration = false,
}]

Examples

Reported:

const width = height = 100;

let first, last;
first = last = items[0];

class Box {
  width = this.height = 100;
}

Not reported:

const width = 100;
const height = 100;

let first, last;
first = items[0];
last = first;

Options

Option	Default	What it does
ignoreNonDeclaration	false	Only report chains in a var, let or const declaration or a class field. Allow them between variables that already exist.

let first, last;
first = last = items[0];

const width = height = 100;