clone&extend.js

const slice = Array.prototype.slice;
const toString = Object.prototype.toString;

function isObject(value) {
  return value !== null && typeof value === 'object';
}

function clone(value, deep) {
    if (isObject(value)) {
        let copy;

        switch (toString.call(value)) {
            case '[object Array]':
                copy = value.slice();
                break;
            case '[object RegExp]':
                copy = new RegExp(value);
                break;
            case '[object Date]':
                copy = new Date(+value);
                break;
            default: 
                copy = {};
        }

        for (let k in value) {
            let v = value[k];
            copy[k] = deep ? clone(v, true) : v;
        }

        return copy;
    }

    return value;
}

function extend(deep, dst, src) {
    if (typeof deep !== 'boolean') {
        src = slice.call(arguments, 1);
        dst = deep;
        deep = false;
    } else {
        src = slice.call(arguments, 2);
    }

    src.forEach(srcObj => {
        for (let k in srcObj) {
            let v = srcObj[k];
            dst[k] = deep ? clone(v, true) : v;
        }
    });

    return dst;
}