This little function deep clones an array, instead of slice which preserves references to objects and nested arrays.

trueClone.js

// Parts of this function were borrowed from http://blog.andrewray.me/how-to-clone-a-nested-array-in-javascript/
// Link to code pen: https://codepen.io/jaspercreel/pen/jLmEWL

function trueClone(item) {
	let copy, i;

	if (Array.isArray(item)) {
		copy = item.slice(0);
		for (i = 0; i < copy.length; i++) {
			copy[i] = trueClone(copy[i]);
		}

		return copy;
	}
	else if (typeof item === 'object') {
		copy = Object.assign({}, item);
    
		for (let prop in copy) {
      			copy[prop] = trueClone(copy[prop]);
		
    		}
    
    		return copy;
	}
	else {
		return item;
	}
}