no-mutating-functions.md

Forbid the use of Object.assign() with a variable as first argument

Object.assign() is a method that mutates its first argument. In order to use this method as a non-mutating method, the first element may not be a variable (even if declared using const), and should therefore be a static value, such as an object expression.

Options

This rule supports the following options:

reducers: An array of method names that are reducer's that are exempt from use function modification.

Fail

var a = {foo: 1, bar: 2};
var b = {bar: 3};
Object.assign(a, b);

Object.defineProperties(object, props);
Object.defineProperty(object, 'prop', descriptor);
Object.setPrototypeOf(object, prototype);

Pass

var a = {foo: 1, bar: 2};
var b = {bar: 3};
Object.assign({}, a, b);
Object.assign({foo: 1, bar: 2}, b);
Object.assign(function foo() {}, {propTypes: {}});