CSS3 and Javascript realize the effect of progress bar

This article mainly introduces Javascript CSS3 to implement the progress bar effect, which can give users a waiting process. If you need it, you can learn more.

Progress bars can be used in many webs. This article introduces the effect of the progress bar. The specific code is as follows:

1: CSS2 attribute clip realizes web page progress Article;

Before implementing, let’s first introduce the clip attribute, because this attribute is rarely used in CSS2.1, so it is necessary for us to understand it;

Browser support: All major browsers support the clip attribute.

The Clip attribute is described on the w3c official website as follows: the visible area of ​​the element is controlled by cropping the element. By default, the element does not undergo any cropping.

The syntax of Clip clipping is as follows:

 .xx {clip:rect(<top>, <right>, <bottom>, <left>)}

The Rect attribute requires four values, top, right, bottom, left; they need to be separated by commas. Follow the clockwise rotation rule, which is the same as the writing order of margin and padding in our CSS.

In css2.1, the offset specified by , of rect() is calculated from the top edge of the element's box, and , is specified. The offset is calculated from the left edge of the element's box. As follows:

We can look at a simple demo again,

The following css

p#one { clip: rect(5px, 40px, 45px, 5px); }
p#two { clip: rect(5px, 55px, 45px, 5px); }

The above example is in a 50X55px rectangular box The middle line is cut, and a dotted rectangle is obtained:

As shown below:

We can now look at a demo of a progress bar;

HTML code is as follows:

<h2>使用clip实现裁剪demo</h2>
<p id="progress-box" class="progress-box">
  <p id="progress-bar" class="progress-bar"></p>
  <p id="progress-text" class="progress-text">0%</p>
</p>

CSS code is as follows:

.progress-box{position:absolute;left:0;width:300px;height:60px;border:1px solid #000;margin-left:20px;}
.progress-bar{position:absolute;left:0;top:0;width:300px;height:60px;clip:rect(0px,0px,60px,0px);background:red;}
.progress-text{position:absolute;left:0;top:0;width:300px;height:60px;color:Black;text-align:center; line-height:60px; font-family:Georgia;font-size:2em;font-weight:bold;}

Here we need to explain the three p's of the above HTML. One is the element container (progress-box), which basically wants to highlight the border and let the user know how long the capacity should be at 100%.

The second progress-bar represents the changing background color of the element set to red,

The third one represents the numerical text representing progress display.

In order to demonstrate the effect, we need a simple setInterval code in JS to demonstrate the effect of the progress bar; the following setInterval code;

var bar = document.getElementById("progress-bar"),
   text = document.getElementById("progress-text");
var cent = 0,
   max = 300;
var timer = setInterval(progressFn, 30);
function progressFn() {
  if(cent > max) {
    cent = 0;
    timer = setInterval(arguments.callee(), 30);
  }else {
    bar.style.clip = "rect(0px," + cent + "px,60px,0px)";
    text.innerHTML = Math.ceil((cent / max) * 100) + "%";
    cent++;
  }
}

The demo effect is as follows; use clip to achieve cropping demo

2: Use progress events (progress) to interact with the server to realize the web page progress bar;

Progress events (progress): Defines events related to client-server communication. There are the following 6 progress events.

1. loadstart: Triggered when the first byte of the corresponding data is received.

2. progress: Triggered continuously during the period of receiving the response.

3. error: Triggered when an error occurs in the request.

4. abort: Triggered when the link is terminated due to calling the abort() method.

5. load: Triggered when complete corresponding data is received.

6. loadend: Triggered after communication is completed or error, abort or load event is triggered.

Each request does not start by triggering the Loadstart event, followed by one or more progress events, then triggering one of the error, abort or load events, and finally ending with the loadend event being triggered.

Browsers that support the first five events include Firefox 3.5, Safari 4, Chrome, Safari for iOS and WebKit for Android.

This event will be triggered periodically while the browser receives new data. The onprogress event handler will receive an event object whose target attribute is the XHR object, but contains three additional attributes: lengthComputable, position, and totalSize. Among them, lengthComputable is a Boolean value indicating whether progress information is available, position indicates the number of bytes received, and totalSize indicates the expected number of bytes determined based on the corresponding Content-Length header. With this information, we can create a progress indicator for the user. The screenshot below has the three parameters introduced above;

The HTML code is as follows:

<h2>使用clip实现裁剪demo</h2>
<p id="progress-box" class="progress-box">
  <p id="progress-bar" class="progress-bar"></p>
  <p id="progress-text" class="progress-text">0%</p>
</p>

The code for interacting with the server is as follows:

var pbar = document.getElementById("progress-bar"),
  pText = document.getElementById("progress-text");
var cent = 0,
  max = 300;
function createXHR(){
   var xhr;
   if (window.XMLHttpRequest){// code for IE7+, Firefox, Chrome, Opera, Safari
     xhr=new XMLHttpRequest();
   }else{ // code for IE6, IE5
     xhr=new ActiveXObject("Microsoft.XMLHTTP");
   }
   return xhr;
 }
 var xhr = createXHR();
 xhr.onload = function() {
  if((xhr.status >= 200 && xhr.status < 300) || xhr.status == 304) {
     alert(xhr.responseText);
  }else {
     alert("Request was unsuccessful: " + xhr.status);
  }
 }
 xhr.onprogress = function(event) {
  var pStatus = document.getElementById("status");
  if (event.lengthComputable) {
      pStatus.innerHTML = "Recived" + event.position + " of " + event.totalSize + " bytes";
      console.log(event.target);
      var percentComplete = Math.round(event.loaded / event.total);
      // 其中的event.loaded表示当前加载了多少字节流，而event.total表示总共有多少字节流 得到这样一个百分比，
      console.log(event.loaded, event.total, 300 * percentComplete);
      progressFn(300 * percentComplete, max);
   }
 }
    
 xhr.open("get", "progress.php", true);
 xhr.send(null); 
 function progressFn(cent,max) {
   if (cent < max) {
     pbar.style.clip = "rect(0px," + cent + "px,60px,0px)";
     pText.innerHTML = Math.ceil((cent / max) * 100) + "%";
   } 
 }

Write any PHP code for casual simulation. Of course, it will definitely be used in actual use. Not so! I just output a content;

<?php
  header("Content-Type: text/plain");
  header("Content-Length: 27");
  echo "Some data";
  flush();
  echo "Some data";
  flush();
  echo "Some data";
  flush();
?>

3: CSS3 animation and linear gradient implementation progress bar demo;

The HTML code is as follows:

<p id="loading-status">
  <p id="process"></p>
</p>

The CSS code is as follows:

#loading-status {width:300px;border:1px solid #669CB8;-webkit-box-shadow: 0px 2px 2px #D0D4D6; -moz-box-shadow:0px 2px 2px #D0D4D6;border-radius: 10px;height:20px;padding: 1px;}
#process {width: 80%;height: 100%;border-radius: 10px;background: -webkit-gradient(linear, 0 0, 0 100%, from(#7BC3FF), color-stop(0.5,#42A9FF), to(#7BC3FF));-webkit-animation: load 3s ease-out infinite;}
@-webkit-keyframes load {
  0% {
    width: 0%;      
  }
  100% {
    width: 80%;    
  }
}

The effect is as follows:

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