Summary of the method of converting js images to base64-JS Tutorial-php.cn

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Summary of the method of converting js images to base64

Jun 02, 2018 am 10:55 AM

base64 javascript Summarize

This time I will bring you a summary of the method of converting js images to base64, and what are the precautions for converting js images to base64. The following is a practical case, let's take a look.

Method 1: Blob and FileReader objects

Implementation principle:

Use xhr to request images, and set the returned file type to Blob object [xhr .responseType = "blob"]

Use FileReader object to receive blob

&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
  &lt;meta charset=&quot;UTF-8&quot;&gt;
  &lt;meta name=&quot;viewport&quot; content=&quot;width=device-width, initial-scale=1.0&quot;&gt;
  &lt;meta http-equiv=&quot;X-UA-Compatible&quot; content=&quot;ie=edge&quot;&gt;
  &lt;title&gt;js 图片转base64方式&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
  &lt;p id=&quot;container1&quot;&gt;&lt;/p&gt;
  &lt;script&gt;
    getBase64("https://z649319834.github.io/Learn_Example/video_track/webvtt.jpg")
    function getBase64(imgUrl) {
      window.URL = window.URL || window.webkitURL;
      var xhr = new XMLHttpRequest();
      xhr.open("get", imgUrl, true);
      // 至关重要
      xhr.responseType = "blob";
      xhr.onload = function () {
        if (this.status == 200) {
          //得到一个blob对象
          var blob = this.response;
          console.log("blob", blob)
          // 至关重要
          let oFileReader = new FileReader();
          oFileReader.onloadend = function (e) {
            let base64 = e.target.result;
            console.log("方式一》》》》》》》》》", base64)
          };
          oFileReader.readAsDataURL(blob);
          //====为了在页面显示图片，可以删除====
          var img = document.createElement("img");
          img.onload = function (e) {
            window.URL.revokeObjectURL(img.src); // 清除释放
          };
          let src = window.URL.createObjectURL(blob);
          img.src = src
          document.getElementById("container1").appendChild(img);
          //====为了在页面显示图片，可以删除====
        }
      }
      xhr.send();
    }
  &lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;

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Method 2: canvas.toDataURL() method

Implementation principle:

Use the canvas.toDataURL() method

Need to solve the cross-domain problem of images image.crossOrigin = '';

Used the $.Deferred() method of the Jquery library

&lt;!DOCTYPE html&gt;
&lt;html lang=&quot;en&quot;&gt;
&lt;head&gt;
  &lt;meta charset=&quot;UTF-8&quot;&gt;
  &lt;meta name=&quot;viewport&quot; content=&quot;width=device-width, initial-scale=1.0&quot;&gt;
  &lt;meta http-equiv=&quot;X-UA-Compatible&quot; content=&quot;ie=edge&quot;&gt;
  &lt;title&gt;js 图片转base64方式&lt;/title&gt;
&lt;/head&gt;
&lt;body&gt;
&lt;p id=&quot;container2&quot;&gt;&lt;/p&gt;
  &lt;script src=&quot;https://apps.bdimg.com/libs/jquery/2.1.1/jquery.min.js&quot;&gt;&lt;/script&gt;
  &lt;script&gt;
    let imgSrc = "https://z649319834.github.io/Learn_Example/video_track/webvtt.jpg";
    //width、height调用时传入具体像素值，控制大小 ,不传则默认图像大小
    function getBase64Image(img, width, height) {
      var canvas = document.createElement("canvas");
      canvas.width = width ? width : img.width;
      canvas.height = height ? height : img.height;
      var ctx = canvas.getContext("2d");
      ctx.drawImage(img, 0, 0, canvas.width, canvas.height);
      var dataURL = canvas.toDataURL();
      return dataURL;
    }
    function getCanvasBase64(img) {
      var image = new Image();
      //至关重要
      image.crossOrigin = '';
      image.src = img;
      //至关重要
      var deferred = $.Deferred();
      if (img) {
        image.onload = function () {
          deferred.resolve(getBase64Image(image));//将base64传给done上传处理
          document.getElementById("container2").appendChild(image);
        }
        return deferred.promise();//问题要让onload完成后再return sessionStorage['imgTest']
      }
    }
    getCanvasBase64(imgSrc)
      .then(function (base64) {
        console.log("方式二》》》》》》》》》",base64);
      }, function (err) {
        console.log(err);
      });
  &lt;/script&gt;
&lt;/body&gt;
&lt;/html&gt;

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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!