jQuery uses FormData to implement file upload-PHP开发-php.cn

Home

php教程

PHP开发

jQuery uses FormData to implement file upload

高洛峰

Dec 06, 2016 pm 01:15 PM

jquery

Foreword

We introduce jQuery for asynchronous uploading to get a better user experience. On the one hand, asynchronous operations in JavaScript are more flexible than forms; on the other hand, asynchronous uploads also avoid long-term page freezes when uploading large files.

HTML

An of type=file allows users to browse and select files. Generally, the input control is placed in a

, a simple form below:

<form>
 <input type="file" id="avatar" name="avatar">
 <button type="button">保存</button>
</form>

Copy after login

But why can I only select one file? ? Add a multiple attribute to to enable multiple selections!

<input type="file" id="avatar" name="avatar" multiple>

Copy after login

Get the file list

The above will have a DOM attribute called files, which contains the selected file list (Array).

$(&#39;button&#39;).click(function(){
 var $input = $(&#39;#avatar&#39;);
 // 相当于： $input[0].files, $input.get(0).files
 var files = $input.prop(&#39;files&#39;);
 console.log(files);
});

Copy after login

Each item in this Array is a File object, which has the following main attributes:

name: file name, read-only string, does not contain any path information.

size : File size, unit is bytes, read-only 64-bit integer.

type: MIME type, read-only string, if the type is unknown, an empty string is returned.

For details, please refer to: https:// developer.mozilla.org/zh-CN/docs/Using_files_from_web_applications

multipart/form-data

Uploading files is special. Its content is binary data, while HTTP provides a text-based communication protocol. In this case, a multipart/form-data encoded HTTP form is required.

The HTTP message body format is as follows:

------WebKitFormBoundaryrGKCBY7qhFd3TrwA
Content-Disposition: form-data; name="title"
 
harttle
------WebKitFormBoundaryrGKCBY7qhFd3TrwA
Content-Disposition: form-data; name="avatar"; filename="harttle.png"
Content-Type: image/png
 
 ... content of harttle.png ...
------WebKitFormBoundaryrGKCBY7qhFd3TrwA--

Copy after login

Each field is separated by a boundary string. The browser ensures that the boundary string does not duplicate the content, so multipart/form-data can successfully encode binary data .

jQuery upload file

This is the FormData object provided by XMLHttpRequest Level 2 that can help us perform multipart/form-data encoding of binary files:

$(&#39;button&#39;).click(function(){
 var files = $(&#39;#avatar&#39;).prop(&#39;files&#39;);
 
 var data = new FormData();
 data.append(&#39;avatar&#39;, files[0]);
 
 $.ajax({
  url: &#39;/api/upload&#39;,
  type: &#39;POST&#39;,
  data: data,
  cache: false,
  processData: false,
  contentType: false
 });
});

Copy after login

url, type, data must be familiar to those who work on the front end , introduce the remaining three parameters:

cache

cache is set to false to prevent the browser from caching the URL (and the corresponding HTTP method). jQuery does this by adding a redundant parameter to the URL.

This method only works for GET and HEAD. However, IE8 will cache the previous GET results to respond to the POST request. Setting cache: false here is for compatibility with IE8.

Reference: http://api.jquery.com/jquery.ajax/

contentType

The default value of content-type in jQuery is application/x-www-form-urlencoded, so the object passed to the data parameter will Converted to query string by default (see HTTP form encoding enctype).

We don’t need jQuery to do this conversion, otherwise it will destroy the encoding format of multipart/form-data. Therefore set contentType: false to disable jQuery's conversion operation.

processData

jQuery will convert the data object into a string to send an HTTP request. By default, application/x-www-form-urlencoded encoding will be used for conversion. The conversion will fail after we set contentType: false, so set processData: false to disable the conversion process.

The data we give is data that has been encoded with FormData, and does not require jQuery for string conversion.

Compatibility and other options

The jQuery file upload method introduced in this article relies on the FormData object. This is the XMLHttpRequest Level 2 interface and requires IE 10+, Firefox 4.0+, Chrome 7+, Safari 5+, Opera 12+

This means that for low-version browsers, you can only directly submit the file form, but the page that submits a large file form will not respond for a long time. If you want to solve this problem in low-version browsers, you can only use other methods. To achieve this, such as many Flash plug-ins that support multiple files and upload progress.

Statement of this Website

The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress images for free

Clothoff.io

AI clothes remover

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

What's New in Windows 11 KB5054979 & How to Fix Update Issues

4 weeks ago By DDD

How to fix KB5055523 fails to install in Windows 11?

3 weeks ago By DDD

InZoi: How To Apply To School And University

4 weeks ago By DDD

How to fix KB5055518 fails to install in Windows 10?

3 weeks ago By DDD

Where to find the Site Office Key in Atomfall

4 weeks ago By DDD

Hot Tools

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Hot Topics

Where is the login entrance for gmail email?

7886

Java Tutorial

1649

CakePHP Tutorial

1410

Laravel Tutorial

1301

PHP Tutorial

1246

Related knowledge

Detailed explanation of jQuery reference methods: Quick start guide Feb 27, 2024 pm 06:45 PM

Detailed explanation of jQuery reference method: Quick start guide jQuery is a popular JavaScript library that is widely used in website development. It simplifies JavaScript programming and provides developers with rich functions and features. This article will introduce jQuery's reference method in detail and provide specific code examples to help readers get started quickly. Introducing jQuery First, we need to introduce the jQuery library into the HTML file. It can be introduced through a CDN link or downloaded

How to use PUT request method in jQuery? Feb 28, 2024 pm 03:12 PM

How to use PUT request method in jQuery? In jQuery, the method of sending a PUT request is similar to sending other types of requests, but you need to pay attention to some details and parameter settings. PUT requests are typically used to update resources, such as updating data in a database or updating files on the server. The following is a specific code example using the PUT request method in jQuery. First, make sure you include the jQuery library file, then you can send a PUT request via: $.ajax({u

In-depth analysis: jQuery's advantages and disadvantages Feb 27, 2024 pm 05:18 PM

jQuery is a fast, small, feature-rich JavaScript library widely used in front-end development. Since its release in 2006, jQuery has become one of the tools of choice for many developers, but in practical applications, it also has some advantages and disadvantages. This article will deeply analyze the advantages and disadvantages of jQuery and illustrate it with specific code examples. Advantages: 1. Concise syntax jQuery's syntax design is concise and clear, which can greatly improve the readability and writing efficiency of the code. for example,

jQuery Tips: Quickly modify the text of all a tags on the page Feb 28, 2024 pm 09:06 PM

Title: jQuery Tips: Quickly modify the text of all a tags on the page In web development, we often need to modify and operate elements on the page. When using jQuery, sometimes you need to modify the text content of all a tags in the page at once, which can save time and energy. The following will introduce how to use jQuery to quickly modify the text of all a tags on the page, and give specific code examples. First, we need to introduce the jQuery library file and ensure that the following code is introduced into the page: &lt

How to remove the height attribute of an element with jQuery? Feb 28, 2024 am 08:39 AM

How to remove the height attribute of an element with jQuery? In front-end development, we often encounter the need to manipulate the height attributes of elements. Sometimes, we may need to dynamically change the height of an element, and sometimes we need to remove the height attribute of an element. This article will introduce how to use jQuery to remove the height attribute of an element and provide specific code examples. Before using jQuery to operate the height attribute, we first need to understand the height attribute in CSS. The height attribute is used to set the height of an element

Use jQuery to modify the text content of all a tags Feb 28, 2024 pm 05:42 PM

Title: Use jQuery to modify the text content of all a tags. jQuery is a popular JavaScript library that is widely used to handle DOM operations. In web development, we often encounter the need to modify the text content of the link tag (a tag) on the page. This article will explain how to use jQuery to achieve this goal, and provide specific code examples. First, we need to introduce the jQuery library into the page. Add the following code in the HTML file:

Understand the role and application scenarios of eq in jQuery Feb 28, 2024 pm 01:15 PM

jQuery is a popular JavaScript library that is widely used to handle DOM manipulation and event handling in web pages. In jQuery, the eq() method is used to select elements at a specified index position. The specific usage and application scenarios are as follows. In jQuery, the eq() method selects the element at a specified index position. Index positions start counting from 0, i.e. the index of the first element is 0, the index of the second element is 1, and so on. The syntax of the eq() method is as follows: $("s

How to tell if a jQuery element has a specific attribute? Feb 29, 2024 am 09:03 AM

How to tell if a jQuery element has a specific attribute? When using jQuery to operate DOM elements, you often encounter situations where you need to determine whether an element has a specific attribute. In this case, we can easily implement this function with the help of the methods provided by jQuery. The following will introduce two commonly used methods to determine whether a jQuery element has specific attributes, and attach specific code examples. Method 1: Use the attr() method and typeof operator // to determine whether the element has a specific attribute

See all articles