js extend

extend-new.js

// ie9+
function extend (target, source) {
    var a = Object.create(target);
    Object.keys(source).map(function (prop) {
        prop in a && (a[prop] = source[prop]);
    });
    return a;
};

extend-old.js

// ltie9
var extend = function ( defaults, options ) {
    var extended = {};
    var prop;
    for (prop in defaults) {
        if (Object.prototype.hasOwnProperty.call(defaults, prop)) {
            extended[prop] = defaults[prop];
        }
    }
    for (prop in options) {
        if (Object.prototype.hasOwnProperty.call(options, prop)) {
            extended[prop] = options[prop];
        }
    }
    return extended;
};