Warning on object assign mutation

object_assign_mutation.js

var a = {
	one: {
		nested: 'a',
		onlyInA: 'a',
		nestedMore: { what: 'a' },
	},
	aOnly: 'a only',
}, b =  {
	one: {
		nested: 'b',
		onlyInB: 'b',
		nestedMore: { what: 'b' },
	},
	bOnly: 'b only',
}, 
// Will copy the reference instead of value of the first argument
// in this case the 'a' variable
c = Object.assign(a,b);
// Which means if you mutate 'c', 'a' will also mutate.
c.aOnly = 'bug from c';
c.bOnly = 'bug from c';
c.one.nested = 'c';
c.one.nestedMore.what = 'c';
console.log(c === a); // true
console.log({a,b,c});

// To avoid this.
// You could either use empty {} object as the first paramater of the Object.assign function
// or use the spread syntax to create a clone (https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Spread_syntax).