How to download pictures using javascript

JavaScript is a widely used scripting language that can be used to create dynamic effects in browsers and servers. Images are a common media type in web applications, so it's important to know how to download images. In this article, we will explore how to download images using JavaScript.

Steps to download images using JavaScript:

Step 1: Get the image URL

To download an image, you first need to obtain the URL of the image. You can use JQuery or native JavaScript to get the src attribute of the image element. For example:

let imageUrl = $('img#myImageId').attr('src');

or

let image = document.getElementById('myImageId');
let imageUrl = image.src;

Step 2: Create an HTTP request

Use the XMLHttpRequest (XHR) object to send an HTTP request to the server and get the response. To download an image, you must create a GET request and give the image's URL as the requested URL. The following is a code example that uses native JavaScript to create an XHR object:

let xhr = new XMLHttpRequest();
xhr.open('GET', imageUrl, true);
xhr.responseType = 'blob';

Note that the responseType attribute is set to 'blob'. This setting indicates that the response should be returned as a Blob object. A Blob object is a file-like binary large object that can be used to process images, audio, and video.

Step 3: Send HTTP request

To send an HTTP request, you need to call the send() method of the XHR object. The following is a code example for sending an HTTP request using native JavaScript:

xhr.onload = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    // 图片下载成功
  }
};

xhr.send();

Note that before calling the send() method, a callback function is registered, which is called after the request is completed. This function can check the request status code and response data to determine whether the image download is successful.

Step 4: Save the image

When the request is successful, the response data needs to be saved as an image file. Blob objects can be read as DataURL strings using a FileReader object.

let reader = new FileReader();
reader.onload = function() {
  let dataUrl = reader.result; // 获取DataURL字符串
  let a = document.createElement('a');
  a.href = dataUrl;
  a.download = 'myImage.jpg'; // 设置文件名
  document.body.appendChild(a);
  a.click(); // 模拟点击下载链接
};

reader.readAsDataURL(xhr.response);

The above code creates a download link that contains the DataURL string as its href attribute. When the user clicks on the link, a file called 'myImage.jpg' is downloaded.

At this point, all steps of downloading images using JavaScript have been completed. The complete code is as follows:

let imageUrl = $('#myImageId').attr('src');
let xhr = new XMLHttpRequest();
xhr.open('GET', imageUrl, true);
xhr.responseType = 'blob';

xhr.onload = function() {
  if (xhr.readyState === 4 && xhr.status === 200) {
    let reader = new FileReader();
    reader.onload = function() {
      let dataUrl = reader.result;
      let a = document.createElement('a');
      a.href = dataUrl;
      a.download = 'myImage.jpg';
      document.body.appendChild(a);
      a.click();
    };

    reader.readAsDataURL(xhr.response);
  }
};

xhr.send();

Summary

This article introduces the steps on how to use JavaScript to download images. It should be noted that before sending an HTTP request, you need to obtain the URL of the image and set the responseType attribute of the XHR object to 'blob'. When the response data is returned, you can use the FileReader object to convert it into a DataURL string and represent it as the href attribute of the download link.

Downloading pictures is a common function in web applications. Images can be easily downloaded and displayed in the browser using JavaScript. The steps described in this article work with most modern web browsers and we hope you find them helpful.

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