prefer-object-spread

The --fix option on the command line can automatically fix some of the problems reported by this rule.

Prefer use of an object spread over Object.assign.

When Object.assign is called using an object literal as the first argument, this rule requires using the object spread syntax instead. This rule also warns on cases where an Object.assign call is made using a single argument that is an object literal, in this case, the Object.assign call is not needed.

Introduced in ES2018, object spread is a declarative alternative which may perform better than the more dynamic, imperative Object.assign.

Rule Details

Examples of incorrect code for this rule:

/*eslint prefer-object-spread: "error"*/

Object.assign({}, foo);

Object.assign({}, {foo: 'bar'});

Object.assign({ foo: 'bar'}, baz);

Object.assign({}, baz, { foo: 'bar' });

Object.assign({}, { ...baz });

// Object.assign with a single argument that is an object literal
Object.assign({});

Object.assign({ foo: bar });

Examples of correct code for this rule:

/*eslint prefer-object-spread: "error"*/

({ ...foo });

({ ...baz, foo: 'bar' });

// Any Object.assign call without an object literal as the first argument
Object.assign(foo, { bar: baz });

Object.assign(foo, bar);

Object.assign(foo, { bar, baz });

Object.assign(foo, { ...baz });

When Not To Use It

This rule should not be used unless ES2018 is supported in your codebase.

Version

This rule was introduced in ESLint 5.0.0-alpha.3.

Resources