the instanceOf function that works with primitive type.

instanceOf.js

function instanceOf(inst, cls) {
    if (inst === null || inst === undefined)
        return false;
    if (typeof cls !== 'function')
        throw new TypeError("Second parameter is not a constructor");
    let instance = inst;
    while (instance.__proto__) {
        if (instance.__proto__ === cls.prototype) {
            return true;
        }
        instance = instance.__proto__;
    }
    return false;
}

1 instanceof Number; // false;
" " instanceof String; // false;

instanceOf(1, Number); // true
instanceOf(' ', String) // true