jQuery's 'extend' method without the rest of jQuery

extend.js

/*!
 * Native JS version of jQuery's $.extend() method
 * (code lifted from jQuery 1.11.1 and slightly modified)
 * native JS implementations of $.isPlainObject(), $.isArray(), $.isFunction()
 * https://gist.github.com/Error601/8fdffa6ff985cc374792
 */

function extend(){

    var src, copyIsArray, copy, name, options, clone,
        target = arguments[0] || {},
        i = 1,
        length = arguments.length,
        deep = false;

    function isPlainObject (obj){
        return Object.prototype.toString.call(obj) === '[object Object]';
    }

    function isArray (arr){
        if ( Array.isArray ) {
            return Array.isArray(arr);
        }
        else {
            return Object.prototype.toString.call(arr) === '[object Array]';
        }
    }

    function isFunction (func){
        return typeof func == 'function';
    }

    // Handle a deep copy situation
    if ( typeof target === "boolean" ) {
        deep = target;

        // skip the boolean and the target
        target = arguments[ i ] || {};
        i++;
    }

    // Handle case when target is a string or something (possible in deep copy)
    if ( typeof target !== "object" && !isFunction(target) ) {
        target = {};
    }

    // extend parent object if only one argument is passed
    if ( i === length ) {
        target = this;
        i--;
    }

    // 'for' loops blow
    while ( i < length ) { 
        // Only deal with non-null/undefined values
        if ( (options = arguments[ i ]) != null ) {
            // Extend the base object
            for ( name in options ) {

                if ( !options.hasOwnProperty(name) ) {
                    continue;
                }

                src = target[ name ];
                copy = options[ name ];

                // Prevent never-ending loop
                if ( target === copy ) {
                    continue;
                }

                // Recurse if we're merging plain objects or arrays
                if ( deep && copy && ( isPlainObject(copy) || (copyIsArray = isArray(copy)) ) ) {

                    if ( copyIsArray ) {
                        copyIsArray = false;
                        clone = src && isArray(src) ? src : [];

                    }
                    else {
                        clone = src && isPlainObject(src) ? src : {};
                    }

                    // Never move original objects, clone them
                    target[ name ] = extend(deep, clone, copy);

                    // Don't bring in undefined values
                }
                else if ( copy !== undefined ) {
                    target[ name ] = copy;
                }
            }
        }
        i++;
    }

    // Return the modified object
    return target;
}