一、单混入(单继承)

function extend(sourceObj, targetObj) {
    for (var key in targetObj) {
        if (targetObj.hasOwnProperty(key)) {
            sourceObj[key] = targetObj[key];
        }
    }
    return sourceObj;
}

二、多继承

function mix() {
    var target = arguments[0];
    for (var i = 1, len = arguments.length; i < len; i++) {
        var arg = arguments[i];
        for (var key in arg) {
            if (arg.hasOwnProperty(key)) {
                target[key] = arg[key];
            }
        }
    }
    return target;
}