Using Promise in JS to implement traffic light example code (demo)-JS Tutorial-php.cn

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Using Promise in JS to implement traffic light example code (demo)

韦小宝

Jan 11, 2018 am 10:16 AM

javascript promise traffic light

This article introduces you to the use of Promise in JS to achieve traffic light effects through example code. It also introduces an example of promise usage. Friends who do not know how to use Promise in JS can refer to this article

Requirements

Use promise to realize the jump of traffic light color
The green light is executed for three seconds After
After the yellow light is executed for four seconds
The red light is executed for five seconds

html implementation As follows:

<ul id="traffic" class="">
 <li id="green"></li>
 <li id="yellow"></li>
 <li id="red"></li>
</ul>

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Define an empty class, and then operate the corresponding class name in js to achieve related effects.

CSS is implemented as follows:

ul {
 position: absolute;
 width: 200px;
 height: 200px;
 top: 50%;
 left: 50%;
 transform: translate(-50%,-50%);
}
 /*画3个圆代表红绿灯*/
 ul >li {
  width: 40px;
  height: 40px;
  border-radius:50%;
  opacity: 0.2;
  display: inline-block;
 }
 /*执行时改变透明度*/
 ul.red >#red, 
 ul.green >#green,
 ul.yellow >#yellow{
  opacity: 1.0;
 }
 /*红绿灯的三个颜色*/
 #red {background: red;}
 #yellow {background: yellow;}
 #green {background: green;}

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javascriptPrinciple:

The promise function is an asynchronous operation function that ends after the function runs You can use the then() method. We can achieve this by setting delayed execution inside the promise function.

js code is as follows:

function timeout(timer){
  return function(){ 
   return new Promise(function(resolve,reject){
   setTimeout(resolve,timer) 
   })  
  }
  }
 var green = timeout(3000);
 var yellow = timeout(4000);
 var red = timeout(5000);
 var traffic = document.getElementById("traffic");
 (function restart(){
  &#39;use strict&#39;      //严格模式
  console.log("绿灯"+new Date().getSeconds()) //绿灯执行三秒 
  traffic.className = &#39;green&#39;;
  green()
  .then(function(){
   console.log("黄灯"+new Date().getSeconds()) //黄灯执行四秒
   traffic.className = &#39;yellow&#39;;
   return yellow();
  })
  .then(function(){
   console.log("红灯"+new Date().getSeconds()) //红灯执行五秒
   traffic.className = &#39;red&#39;;
   return red();
  }).then(function(){
   restart()
  })
  })();

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ps: Let’s look at an example of Promise usage

Note: If you want the then method to If the chain execution continues, the Promise object must be returned! ! !

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&#39;use strict&#39;; 
  
function async(value) { 
  return new Promise(function(resolve, reject) { 
    var ms = Math.round(Math.random() * 1000); 
    setTimeout(function() { 
      console.log(&#39;waiting &#39; + ms + &#39;ms&#39;); 
      // 等待ms毫秒 
      resolve(value + ms); 
    }, ms); 
  }); 
} 
// 每次执行随机等待n毫秒，结果统计总毫秒数 
async(0) 
.then(async) 
.then(async) 
.then(async) 
.then(async) 
.then(function(value) { 
  console.log(&#39;------total wait:&#39; + value + &#39;ms&#39;); 
}); 
//////////////////////////////////////////////////////////// 
function async1(value) { 
  return new Promise(function(resolve, reject) { 
    resolve(value + 1); 
  }); 
} 
function async2(value) { 
  // return new Promise(function(resolve, reject) { 
  //   resolve(value + 2); 
  // }); 
  // 等价与上面写法 
  return Promise.resolve(value + 2); 
} 
function async3(value) { 
  return new Promise(function(resolve, reject) { 
    resolve(value + 3); 
  }); 
} 
async1(100).then(async2).then(async3).then(function(value) { 
  console.log(&#39;------&#39; + value); 
}); 
///////////////////////////////////////////////////////////////// 
function say() { 
  var value = &#39;what&#39;; 
  return Promise.resolve(value); 
} 
say().then(function(value) { 
  value = value + &#39; are&#39;; 
  return Promise.resolve(value); 
}).then(function(value) { 
  value = value + &#39; you&#39;; 
  return Promise.resolve(value); 
}).then(function(value) { 
  value = value + &#39; doing&#39;; 
  return Promise.resolve(value); 
  //return Promise.reject(&#39;error, exit&#39;); // 中途退出 
}).then(function(value) { 
  value = value + &#39; now!&#39;; 
  return Promise.resolve(value); 
}).then(function(value) { 
  console.log(&#39;------&#39; + value); 
}).catch(function(error) { 
  console.log(&#39;------&#39; + error); 
}); 
<html> 
<head> 
  <title>Ball move</title> 
  <style type="text/css"> 
    .ball { 
      width: 40px; 
      height: 40px; 
      border-radius: 20px; 
      margin-left: 10px; 
    } 
    .ball1 { 
      background: #ff0000; 
    } 
    .ball2 { 
      background: #00ff00; 
    } 
    .ball3 { 
      background: #0000ff; 
    } 
  </style> 
  <script src="http://libs.baidu.com/jquery/1.9.0/jquery.js"></script> 
</head> 
<body> 
  <p class="ball ball1"></p> 
  <p class="ball ball2"></p> 
  <p class="ball ball3"></p> 
  <script type="text/javascript"> 
    function moving(ball, pos) { 
      return new Promise(function(resolve, reject) { 
        var marginLeft = parseInt(ball.css(&#39;margin-left&#39;)); 
        if (marginLeft != pos) { 
          var timerId = setInterval(function() { 
            marginLeft = marginLeft + 1; 
            ball.css(&#39;margin-left&#39;, marginLeft); 
            if (marginLeft == pos) { 
              clearInterval(timerId); 
              resolve(); 
            } 
          }, 20); 
        } else { 
          resolve(); 
        } 
      }); 
    } 
    moving($(&#39;.ball1&#39;), 100).then(function() { 
      return moving($(&#39;.ball2&#39;), 150); 
    }).then(function() { 
      return moving($(&#39;.ball3&#39;), 200); 
    }); 
  </script> 
</body> 
</html>

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The above is the example code (demo) of using Promise to implement traffic lights in JS introduced by the editor. I hope it will be helpful to everyone! !

Related recommendations:

The specific method of using Promise in jQuery

How to implement a complete Promise

About the simple usage of promise objects

The above is the detailed content of Using Promise in JS to implement traffic light example code (demo). For more information, please follow other related articles on the PHP Chinese website!

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