[js] 闭包(old)

1.取函数内部的变量
2.让变量的值保持在内存中(滥用可能会导致内存泄漏)

 

 

 

#立即调用的函数表达式的各种写法 (IIFE)

// jshint expr: true

(function() {
    // child scope
})();

!function () {
    // child scope
}();

+function () {
    // child scope
}();

-function () {
    // child scope
}();

~function () {
    // child scope
}();

void function () {
    // child scope
}();

// maybe you're feeling whacky (hint: don't use these)

1^function () {
    // child scope
}();

1&function () {
    // child scope
}();

 #

            (function(window) {
                var lastId = 0;
                var data = {};

                function Lib() {
                    var id = ++lastId;
                    Object.defineProperty(this, '_id', {
                        value: id
                    }); //freeze
                    data[this._id] = {
                        state: 'idle'
                    };
                    this.delay = 3000;
                }
                Lib.prototype.version = '0.0.1';
                Lib.prototype.waitForNoReason = function(method) {
                    data[this._id].state = 'waiting';
                    window.setTimeout(then.bind(this), this.delay);

                    function then() {
                        data[this._id].state = 'executing';
                        var update = done.bind(this);
                        method(update);
                    }
                };

                function done() {
                    data[this._id].state = 'done';
                }
                Lib.prototype.getState = function() {
                    return data[this._id].state;
                };
                window.Lib = Lib;
            })(window);
            var instance = new Lib();
            instance._id = 30; //不能改变
            console.log(instance._id);
            // 1
            console.log(instance.version);
            // '0.0.1'
            console.log(instance.delay);
            // 3000
            console.log(instance.getState());
            // <- 'idle'
            instance.waitForNoReason(function(done) {
                console.log(instance.getState());
                // 'executing'
                done();
                console.log(instance.getState());
                // 'done'
            });
            console.log(instance.getState());
            // 'waiting'
            //1
            //0.0.1
            //3000
            //idle
            //waiting
            //executing
            //done

 #

            var Cat = (function() {
                var sw = 0,
                    count = 0;

                function o(name, weight) {
                    if (!name || !weight) {
                        throw 'error';
                    }
                    count++;
                    console.warn(count);
                    this.name = name;
                    w = weight;
                    sw += w;
                    Object.defineProperty(this, "weight", {
                        set: function(newValue) {
                            //设置属性触发
                            sw += newValue - w;
                            w = newValue;
                        },
                        get: function() {
                            return w;
                        },
                        enumerable: true,
                        configurable: true
                    });
                }
                //console.info(sw, count);这里读取不到属性
                o.averageWeight = function() {
                        console.info(sw, count);
                        return sw / count;
                    } //用了prototype会被外部检测到详情。这里相当于一个对象属性
                return o;
            }());
            fluffy = new Cat('fluffy', 15);
            console.log(fluffy.name);
            console.log(fluffy.weight);
            //console.log(fluffy.averageWeight());
            console.log(fluffy instanceof Cat);
            console.log(fluffy.averageWeight);
            console.log(typeof Cat.averageWeight);
            console.log(Cat.averageWeight());
            garfield = new Cat('garfield', 25);
            console.log(garfield.name);
            console.log(garfield.weight);
            //console.log(garfield.averageWeight());
            console.log(Cat.averageWeight());
            garfield.weight = 35;
            console.warn(garfield.name);
            console.log(garfield.weight);
            //console.log(garfield.averageWeight());
            console.log(Cat.averageWeight());

 

#保存局部变量

    <body>
        <ul id='test'>
            <li>这是第一条</li>
            <li>这是第二条</li>
            <li>这是第三条</li>
            <li>这是第四条</li>
        </ul>
        <script>
            var list = document.getElementById("test").getElementsByTagName('li');
            for (var i = 0; i < list.length; i++) {
                list[i].addEventListener('click', (function(a) {
                    return function() {
                        console.log(a);
                    }
                })(i))
            }
        </script>
    </body>