Detailed explanation of the steps of the native JS encapsulation fade-in and fade-out effect function-JS Tutorial-php.cn

Detailed explanation of the steps of the native JS encapsulation fade-in and fade-out effect function

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Release： 2018-05-10 10:38:54

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This time I will bring you a detailed explanation of the steps of the native JS encapsulated fade-in and fade-out effect function. What are the precautions for the native JS encapsulated fade-in and fade-out effect function. The following is a practical case, let’s take a look.

When it comes to the gradient display and disappearance of js, most friends will think of fadeIn(), fadeOut() or fadeToggle() in JQuery. But what if the huge JQuery library is called just to introduce such an effect? In other words, I improved myself by using native js to implement some functions~

So, I briefly studied the effect of writing fade-in and fade-out in pure js code.

If there is an error, please point it out in the comments so that I can correct my own mistakes

(1) FadeIn Function

The fade-in and fade-out effect is actually a setInterval(), plus a cyclic DOM operation, which can be achieved by changing the transparency of the element object node. kind of effect.

So we extract two necessary things: setInterval(), opacity, and speed.

speed: This is the float value change speed when we set the opacity value from 0 to 1.
The logic of fading in: the opacity value changes from 0 to 1. Float value changes from 0 to 1.

Let’s look at the code implementation first!

html:

<p id="p1"></p>
<span id="span1">123</span>
<button>fadein</button>
<button>fadeOut</button>

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css style

<style>
 p {
  width: 100px;
  height: 100px;
  background-color: #1d7db1;
  opacity:0;
 }
 </style>

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First of all, let’s look at how to write the first version of the fadeIn function: first understand the idea of implementation

function fadeIn(ele, speed) {
  let num = 0;
  let time = setInterval(() => {
    num += speed;
    ele.style.opacity = num / 100;
    if (num >= 100) {
     clearInterval(time); // 清楚定时器
    }
  }, 30);
  }
}

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When this effect is temporarily achieved, some things are not that simple. If multiple trigger effects occur, setInterval will be used multiple times at the same time, causing some troublesome BUGs.

To solve this problem, there is currently a solution: add a global state to prevent setInterval from being triggered multiple times.

let Fadeflag = true;
function fadeIn(ele, speed) {
  let num = 0;
  if (Fadeflag) {
  let time = setInterval(() => {
    num += speed;
    Fadeflag = false;
    ele.style.opacity = num / 100;
    if (num >= 100) {
     clearInterval(time);
     Fadeflag = true;
    }
  }, 30);
  }
}

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Compatibility issue! ! !

Look at the code first

set: function(elem, num) {
  elem.style.opacity !== undefined ? elem.style.opacity = num / 100 : elem.style.filter = 'alpha(opacity = '+ num +')';
}

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Note: The code setting num/100 is because we use ie as the standard to be compatible with ff and GG

Set DOM node in jsTransparency function attribute: filter= "alpha(opacity=" value ")" (compatible with ie)

The filter range of ie is 0~100

opacity=value/100 (compatible with ie) FF and GG).

The opacity of FF and GG is 0~1 (in order to be compatible with the filter range of ie, we use num/100)

(2) FadeOut function

speed: This is the speed at which the float value changes when we set the opacity value from 1 to 0 (remember to consider compatibility)

Fade out logic: the opacity value changes from 1 to 0 The float value changes.

Encapsulation function

(function() {
  let fadeFlag = true;
  function Fade(selector) {
    this.elem = typeof selector == 'Object' ? selector : document.getElementById(selector);
  }
  Fade.prototype = {
   constructor: Fade,
    setOpacity: (elem, opacity) => { // 兼容ie10—
      elem.filters ? elem.style.filter = 'alpha(opacity = '+ opacity +')':  elem.style.opacity = opacity / 100;
      return true;
   },
   setOpacity: function(num) {
      this.elem.style.opacity !== undefined ? this.elem.style.opacity = num / 100 : this.elem.style.filter = 'alpha(opacity = '+ num +')';
   },
    fadeIn: function(speed, opacity){
   /*
   speed ==>淡入的速度，正整数（可选）;
   opacity ==>淡入到指定的透明度，0～100（可选）;
      */
      speed = speed || 2;
      opacity = opacity || 100;
      let num = 0; // 初始化透明度变化值为0
      if (fadeFlag) {
        let time = setInterval(() => {
          num += speed;
          fadeFlag = false;
          this.setOpacity(num);
          this.elem.style.opacity !== undefined ? this.elem.style.opacity = num / 100 : this.elem.style.filter = 'alpha(opacity = '+ num +')';
          if (num >= opacity) {
            clearInterval(time);
            fadeFlag = true;
          }
        }, 20);
      }
    },
    fadeOut: function(speed, opacity) {
   /*
   speed ==>淡入的速度，正整数（可选）;
   opacity ==>淡入到指定的透明度，0～100（可选）;
   */
      speed = speed || 2;
      opacity = opacity || 0;
      let num = 100; // 初始化透明度变化值为0
      if (fadeFlag) {
        let time = setInterval(() => {
          num -= speed;
          fadeFlag = false;
          this.set(num);
          this.elem.style.opacity !== undefined ? this.elem.style.opacity = num / 100 : this.elem.style.filter = 'alpha(opacity = '+ num +')';
          if (num <= opacity) {
          clearInterval(time);
          fadeFlag = true;
          }
        }, 20);
      }
    }
  };
window.Fade = Fade;
})();

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Test example:

let btn = document.getElementsByTagName(&#39;button&#39;)[0];
 let btn2 = document.getElementsByTagName(&#39;button&#39;)[1];
 btn.onclick = () => {
  let fade = new Fade('p1');
 fade.fadeIn();
 };
 btn2.onclick = () => {
  let fade = new Fade('p1');
  fade.fadeOut();
 }

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I believe you have mastered the method after reading the case in this article. For more exciting information, please pay attention to other related articles on the PHP Chinese website!