Does it mutate 😱

Array.prototype.toSource()

No mutation

Description

The toSource() method returns a string representing the source code of the array.

arr.toSource()

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/toSource

Example

var alpha = new Array('a', 'b', 'c');

alpha.toSource();
//returns ['a', 'b', 'c']