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Ajax upload file progress bar Codular

亚连
亚连Original
2018-05-22 14:49:101432browse

This article mainly introduces the relevant information of Ajax upload file progress bar Codular. Friends who need it can refer to it

Now, people like to do other things while browsing the web without leaving the web page. Usually it is achieved through ajax. Most of the time, people use jQuery to achieve it, but with the advancement of browsers, people don't need to do this. Here we will introduce how to upload files to the server without leaving the page, We will use the same backend PHP code we used in our previous article. The script will upload the file to the server, display the upload progress, and eventually return the link address of the uploaded file. In some cases, you may want to Return the id of the uploaded file or other application information. Note: This code does not support older IE browsers. We only support IE10 through Can I use

Let's Code

We'll start with the HTML structure, then the JavaScript, and then I'll give you the PHP code, which is adapted from the previous tutorial - there won't be much explanation of the PHP code.

HTML

We only need to use two input boxes, one is the file type file, and the other is just a button button, so that we can listen to it being clicked to send File upload request. We'll also have a p that we change the width to highlight the status of the upload.

As shown below:

<!doctype html>
<html>
<head>
  <meta charset="utf-8">
  <title>JS File Upload with Progress</title>
  <style>
  .container {
    width: 500px;
    margin: 0 auto;
  }
  .progress_outer {
    border: 1px solid #000;
  }
  .progress {
    width: 20%;
    background: #DEDEDE;
    height: 20px; 
  }
  </style>
</head>
<body>
  <p class=&#39;container&#39;>
    <p>
      Select File: <input type=&#39;file&#39; id=&#39;_file&#39;> <input type=&#39;button&#39; id=&#39;_submit&#39; value=&#39;Upload!&#39;>
    </p>
    <p class=&#39;progress_outer&#39;>
      <p id=&#39;_progress&#39; class=&#39;progress&#39;></p>
    </p>
  </p>
  <script src=&#39;upload.js&#39;></script>
</body>
</html>

You will see that we wrote a little progress bar style and added a script file at the bottom to handle file upload and progress bar display.

JavaScript

First, we need to get the tags we are going to use, they have been marked with id.

var _submit = document.getElementById(&#39;_submit&#39;), 
_file = document.getElementById(&#39;_file&#39;), 
_progress = document.getElementById(&#39;_progress&#39;);

Next step, add a click event to _submit, use to upload the file of our choice. To do this, we will use the addEventListener method and let it call the upload method after clicking the button.

_submit.addEventListener(&#39;click&#39;, upload);

Now we can continue to process the upload, there are the following steps:

  1. Check the selected file

  2. Dynamicly create the file data to be sent

  3. Create XMLHttpRequest through js

  4. Upload file

Check the selected file

Our file input box _file has a query Select the file queue parameter files-if you set the multiple parameter, you can select multiple files. We do a simple check and judge. If the array length is greater than 0, continue, otherwise return directly. 

if(_file.files.length === 0){
  return;
}

Now, We can ensure that a file is selected, we will assume that there is a file, please remember that the index of the array starts with 0.

Dynamicly create the file data to be sent

To do this, we need to use FormData and add the data to it. Next, we can send our FormData in the request generated in step 3. The append method we use, the first parameter is similar to the name attribute of the input box, The second parameter is the value value. Here, we set value to the first file we selected.

var data = new FormData();
data.append(&#39;SelectedFile&#39;, _file.files[0]);

We will use this when sending data to the server later.

Creating XMLHttpRequest via upload script

This part is very basic, we will create a new XMLHttpRequest and set some settings. First we will modify the value of onreadystatechange to define the callback function when requesting a state change. This method will check readyState when the state changes to make sure the value is what we want - in this case it is 4, Represents the request completion.

In the second step, we will add the progress event on the upload attribute. In this way, we can get the upload progress to update the progress bar. 

var request = new XMLHttpRequest();
request.onreadystatechange = function(){
  if(request.readyState == 4){
    try {
      var resp = JSON.parse(request.response);
    } catch (e){
      var resp = {
        status: &#39;error&#39;,
        data: &#39;Unknown error occurred: [&#39; + request.responseText + &#39;]&#39;
      };
    }
    console.log(resp.status + &#39;: &#39; + resp.data);
  }
};

When the request is successful, we use try...catch wraps the process of parsing the return value. If the parsing fails, we will create our own return object so that the subsequent code will not report an error. You can decide how to handle the return value. Here we just output it to the console. .

Now let’s deal with the progress bar:

request.upload.addEventListener(&#39;progress&#39;, function(e){
  _progress.style.width = Math.ceil(e.loaded/e.total) * 100 + &#39;%&#39;;
}, false);

It’s a little complicated here. We listen to an event. The event object has two properties that we are more concerned about. loaded and total.loaded represent the values ​​that have been uploaded to the server, and total represents the total value to be sent. We can calculate a percentage based on these two values ​​to set the width of the progress bar.

Note: There is no addition here Any animation effect, but you can customize the animation effect according to your needs.

Upload file

Now we can send the request, we will make a POST request to a file called upload .php file and use the send() method with the parameter data so that we can send the data:

request.open(&#39;POST&#39;, &#39;upload.php&#39;);
request.send(data);

The complete JavaScript code is given below:

var _submit = document.getElementById(&#39;_submit&#39;), 
_file = document.getElementById(&#39;_file&#39;), 
_progress = document.getElementById(&#39;_progress&#39;);
var upload = function(){
  if(_file.files.length === 0){
    return;
  }
  var data = new FormData();
  data.append('SelectedFile', _file.files[0]);
  var request = new XMLHttpRequest();
  request.onreadystatechange = function(){
    if(request.readyState == 4){
      try {
        var resp = JSON.parse(request.response);
      } catch (e){
        var resp = {
          status: 'error',
          data: 'Unknown error occurred: [' + request.responseText + ']'
        };
      }
      console.log(resp.status + ': ' + resp.data);
    }
  };
  request.upload.addEventListener('progress', function(e){
    _progress.style.width = Math.ceil(e.loaded/e.total) * 100 + '%';
  }, false);
  request.open('POST', 'upload.php');
  request.send(data);
}
_submit.addEventListener(&#39;click&#39;, upload);

Now to PHP.. .

PHP

This is the code we use, you will notice some differences, mainly that we use the top JSON method to return the values ​​as JSON format Output. This PHP is the same as the code in the previous article, which means that this method only applies to PNG images smaller than 500Kb. In addition, the success message will return the path of the uploaded file: 

<?php
// Output JSON
function outputJSON($msg, $status = &#39;error&#39;){
  header(&#39;Content-Type: application/json&#39;);
  die(json_encode(array(
    &#39;data&#39; => $msg,
    &#39;status&#39; => $status
  )));
}
// Check for errors
if($_FILES[&#39;SelectedFile&#39;][&#39;error&#39;] > 0){
  outputJSON(&#39;An error ocurred when uploading.&#39;);
}
if(!getimagesize($_FILES[&#39;SelectedFile&#39;][&#39;tmp_name&#39;])){
  outputJSON(&#39;Please ensure you are uploading an image.&#39;);
}
// Check filetype
if($_FILES[&#39;SelectedFile&#39;][&#39;type&#39;] != &#39;image/png&#39;){
  outputJSON(&#39;Unsupported filetype uploaded.&#39;);
}
// Check filesize
if($_FILES[&#39;SelectedFile&#39;][&#39;size&#39;] > 500000){
  outputJSON(&#39;File uploaded exceeds maximum upload size.&#39;);
}
// Check if the file exists
if(file_exists(&#39;upload/&#39; . $_FILES[&#39;SelectedFile&#39;][&#39;name&#39;])){
  outputJSON(&#39;File with that name already exists.&#39;);
}
// Upload file
if(!move_uploaded_file($_FILES[&#39;SelectedFile&#39;][&#39;tmp_name&#39;], &#39;upload/&#39; . $_FILES[&#39;SelectedFile&#39;][&#39;name&#39;])){
  outputJSON(&#39;Error uploading file - check destination is writeable.&#39;);
}
// Success!
outputJSON(&#39;File uploaded successfully to "&#39; . &#39;upload/&#39; . $_FILES[&#39;SelectedFile&#39;][&#39;name&#39;] . &#39;".&#39;, &#39;success&#39;);

The above is me I compiled it for everyone, I hope it will be helpful to everyone in the future.

Related articles:

jQuery Validator verifies Ajax form submission method and Ajax parameter passing method (graphic tutorial)

Ajax asynchronous request technology example explanation

The principle of Ajax cross-domain request (picture and text tutorial)

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