Object.assign(…as) changes input parameter

Question

Object.assign(...as) appears to change the input parameter. Example:

const as = [{a:1}, {b:2}, {c:3}];
const aObj = Object.assign(...as);
         


        

Answer 1

Object.assign is not a pure function, it writes over its first argument target.

Here is its entry on MDN:

Object.assign(target, ...sources)

Parameters

target

The target object — what to apply the sources’ properties to, which is returned after it is modified.

sources

The source object(s) — objects containing the properties you want to apply.

Return value

The target object.

The key phrase is "[the target] is returned after it is modified". To avoid this, pass an empty object literal {} as first argument:

const aObj = Object.assign({}, ...as);