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如何实现一个LazyMan?

3月份找实习的时候,微信面试官给了我一套笔试题,今天整理时无意中翻了出来,其中有一道题特别有意思:

实现一个LazyMan,可以按照以下方式调用:
LazyMan(“Hank”)输出:
Hi! This is Hank!

LazyMan(“Hank”).sleep(10).eat(“dinner”)输出
Hi! This is Hank!
//等待10秒..
Wake up after 10
Eat dinner~

LazyMan(“Hank”).eat(“dinner”).eat(“supper”)输出
Hi This is Hank!
Eat dinner~
Eat supper~

LazyMan(“Hank”).sleepFirst(5).eat(“supper”)输出
//等待5秒
Wake up after 5
Hi This is Hank!
Eat supper
以此类推。

这是典型的JavaScript流程控制,问题的关键是如何实现任务的顺序执行。在Express有一个类似的东西叫中间件,这个中间件和我们这里的吃饭、睡觉等任务很类似,每一个中间件执行完成后会调用next()函数,这个函数用来调用下一个中间件。

对于这个问题,我们也可以利用相似的思路来解决,首先创建一个任务队列,然后利用next()函数来控制任务的顺序执行:

function _LazyMan(name) {
    this.tasks = [];   
    var self = this;

    var fn =(function(n){
        var name = n;
        return function(){
            console.log("Hi! This is " + name + "!");
            self.next();
        }
    })(name);
    this.tasks.push(fn);
    setTimeout(function(){
        self.next();
    }, 0); // 在下一个事件循环启动任务
}

/* 事件调度函数 */
_LazyMan.prototype.next = function() { 
    var fn = this.tasks.shift();
    fn && fn();
}

_LazyMan.prototype.eat = function(name) {
    var self = this;
    var fn =(function(name){
        return function(){
            console.log("Eat " + name + "~");
            self.next()
        }
    })(name);
    this.tasks.push(fn);
    return this; // 实现链式调用
}

_LazyMan.prototype.sleep = function(time) {
    var self = this;
    var fn = (function(time){
        return function() {
            setTimeout(function(){
                console.log("Wake up after " + time + "s!");
                self.next();
            }, time * 1000);
        }
    })(time);
    this.tasks.push(fn);
   return this;
}

_LazyMan.prototype.sleepFirst = function(time) {
    var self = this;
    var fn = (function(time) {
        return function() {
            setTimeout(function() {
                console.log("Wake up after " + time + "s!");
                self.next();
            }, time * 1000);
        }
    })(time);

    this.tasks.unshift(fn);
    return this;
}

/* 封装 */
function LazyMan(name){
    return new _LazyMan(name);
}
编辑于 2016-09-10

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