关于Promise的一个案例

题目：红灯三秒亮一次，绿灯一秒亮一次，黄灯2秒亮一次；如何让三个灯不断交替重复亮灯？（用Promise实现）

解答思路一:

function red(){
    console.log('red');
}
function green(){
    console.log('green');
}
function yellow(){
    console.log('yellow');
}

var tic = function(timmer, cb){
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            cb();
            resolve();
        }, timmer);
    });
};

var d = new Promise(function(resolve, reject){resolve();});
var step = function(def) {
    def.then(function(){
        return tic(3000, red);
    }).then(function(){
        return tic(2000, green);
    }).then(function(){
        return tic(1000, yellow);
    }).then(function(){
        step(def);
    });
}

step(d);

解答思路二:

// 方法二:虽然Promise可以用来解决回调地狱问题，但是仍然不可避免的会有回调出现
var tic = function(timmer, str){
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            console.log(str);
            resolve(1);
        }, timmer);
    });
};

function *gen(){
    yield tic(3000, 'red');
    yield tic(1000, 'green');
    yield tic(2000, 'yellow');
}

var iterator = gen();
var step = function(gen, iterator){
    var s = iterator.next();
    if (s.done) {
        step(gen, gen());
    } else {
        s.value.then(function() {
            step(gen, iterator);
        });
    }
}

step(gen, iterator);

摘录来源:http://www.cnblogs.com/dojo-lzz/p/5495671.html