writing mutable object safely

mutableSet.js

/**
 * 
 * @param o Object to mutate
 * @param ks array of keys, or string of keys
 * @param v value to assign
 * @param sep custom separator if keys is string. ex: ks:"INIxxADALAHxxKEY", sep is: "xx"
 */
function mutableSet(o, ks, v, sep = '.') {
	ks.split && (ks=ks.split(sep));
	let i=0, l=ks.length, t=o, x, k;
	while (i < l) {
		k = ks[i++];
		if (k === '__proto__' || k === 'constructor' || k === 'prototype') break;
		t = t[k] = (i === l) ? v : (typeof(x=t[k])===typeof(ks)) ? x : (ks[i]*0 !== 0 || !!~(''+ks[i]).indexOf(sep)) ? {} : [];
	}
}

upgrade version of https://gist.github.com/ilhamgusti/83bed418013bf0fd2eae8023ed47e9bb