New rule: no-mutating-assign

Description:

Warns when Object.assign is used with the first parameter anything else than object initialisation.

Will warn:

const foo = {};

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

Will not warn:

const foo = {};

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

[jfmengels]

Seeing as there is no maintenance of the plugin, I’ve written my own that has this rule.

[ljharb]

Object.assign does return a value - the first argument. In addition, spread syntax is not yet standard - it’s only stage 1.

I would love this rule, as we use Object.assign({}, …) all the time, but never want the first argument to be anything but a new empty object.