Question

<input type="file" id="asd"/>

一旦用户选择（在提交表单之前），我想在 base64 中获取图片

类似的东西：

$(input).on('change',function(){
  var data = $(this).val().base64file(); // it is not a plugin is just an example
  alert(data);
});

我读过有关File API和其他内容的文章，我想要一个简单的跨浏览器解决方案（明显排除IE6 / IE7）

任何帮助表示感谢。

Answer 1

function readFile() {
  
  if (this.files && this.files[0]) {
    
    var FR= new FileReader();
    
    FR.addEventListener("load", function(e) {
      document.getElementById("img").src       = e.target.result;
      document.getElementById("b64").innerHTML = e.target.result;
    }); 
    
    FR.readAsDataURL( this.files[0] );
  }
  
}

document.getElementById("inp").addEventListener("change", readFile);

<input id="inp" type='file'>
<p id="b64"></p>
<img id="img" height="150">

_{（ P.S：一个base64编码的图像（String）4/3原始图像数据的大小）}

Check this answer for multiple images upload

浏览器支持：http://caniuse.com/#search=file%20api
更多信息：https://developer.mozilla.org/en-US/docs/Web/API/FileReader

Answer 2

你需要什么:)你可以选择回调版或Promise版。请注意，promises只能在IE中使用Promise polyfill lib。您可以在页面上放置一次此代码，此函数将出现在您的所有文件中。

当加载进度停止时会触发loadend事件资源（例如在“错误”，“中止”或“加载”之后）调度）

回调版

        File.prototype.convertToBase64 = function(callback){
                var reader = new FileReader();
                reader.onloadend = function (e) {
                    callback(e.target.result, e.target.error);
                };   
                reader.readAsDataURL(this);
        };

        $("#asd").on('change',function(){
          var selectedFile = this.files[0];
          selectedFile.convertToBase64(function(base64){
               alert(base64);
          }) 
        });

承诺版

    File.prototype.convertToBase64 = function(){
         return new Promise(function(resolve, reject) {
                var reader = new FileReader();
                reader.onloadend = function (e) {
                    resolve({
                      fileName: this.name,
                      result: e.target.result, 
                      error: e.target.error
                    });
                };   
                reader.readAsDataURL(this);
        }.bind(this)); 
    };

    FileList.prototype.convertAllToBase64 = function(regexp){
      // empty regexp if not set
      regexp = regexp || /.*/;
      //making array from FileList
      var filesArray = Array.prototype.slice.call(this);
      var base64PromisesArray = filesArray.
           filter(function(file){
             return (regexp).test(file.name)
           }).map(function(file){
             return file.convertToBase64();
           });
      return Promise.all(base64PromisesArray);
    };

    $("#asd").on('change',function(){
      //for one file
      var selectedFile = this.files[0];
      selectedFile.convertToBase64().
          then(function(obj){
            alert(obj.result);
          });
      });
      //for all files that have file extention png, jpeg, jpg, gif
      this.files.convertAllToBase64(/\.(png|jpeg|jpg|gif)$/i).then(function(objArray){
            objArray.forEach(function(obj, i){
                  console.log("result[" + obj.fileName + "][" + i + "] = " + obj.result);
            });
      });
    })

HTML

<input type="file" id="asd" multiple/>

Answer 3

在这种情况下使用Deferred Object并返回承诺是有用的：

function readImage(inputElement) {
    var deferred = $.Deferred();

    var files = inputElement.get(0).files;
    if (files && files[0]) {
        var fr= new FileReader();
        fr.onload = function(e) {
            deferred.resolve(e.target.result);
        };
        fr.readAsDataURL( files[0] );
    } else {
        deferred.resolve(undefined);
    }

    return deferred.promise();
}

以上功能可以这样使用：

var inputElement = $("input[name=file]");
readImage(inputElement).done(function(base64Data){
    alert(base64Data);
});

或者在你的情况下：

$(input).on('change',function(){
  readImage($(this)).done(function(base64Data){ alert(base64Data); });
});

Answer 4

CLIPS> (defglobal ?*id* = 0)
CLIPS> 
(deffunction next-id ()
   (bind ?*id* (+ ?*id* 1)))
CLIPS> 
(deftemplate employee
   (slot employee-id (default-dynamic (next-id)))
   (slot employee-name)
   (slot Role)
   (slot Designation))
CLIPS> 
(deffacts Employees
   (employee (employee-name X) (Role CS) (Designation TA))
   (employee (employee-name Y) (Role CS) (Designation SA))
   (employee (employee-name Z) (Role CIS) (Designation TA))
   (employee (employee-name W) (Role SE) (Designation SA))
   (employee (employee-name Q) (Role CIS) (Designation TA))
   (employee (employee-name U) (Role CS) (Designation TA)))
CLIPS> (reset)
CLIPS> (facts)
f-0     (initial-fact)
f-1     (employee (employee-id 1) (employee-name X) (Role CS) (Designation TA))
f-2     (employee (employee-id 2) (employee-name Y) (Role CS) (Designation SA))
f-3     (employee (employee-id 3) (employee-name Z) (Role CIS) (Designation TA))
f-4     (employee (employee-id 4) (employee-name W) (Role SE) (Designation SA))
f-5     (employee (employee-id 5) (employee-name Q) (Role CIS) (Designation TA))
f-6     (employee (employee-id 6) (employee-name U) (Role CS) (Designation TA))
For a total of 7 facts.
CLIPS>

Answer 5

// https://developer.mozilla.org/en-US/docs/Web/API/FileReader/readAsDataURL

/* Simple */
function previewImage( image, preview, string )
{

    var preview     = document.querySelector( preview );
    var fileImage   = image.files[0];

    var reader      = new FileReader();

    reader.addEventListener( "load", function() {

        preview.style.height    = "100";
        preview.title           = fileImage.name;

        // convert image file to base64 string
        preview.src             = reader.result;

        /* --- */

        document.querySelector( string ).value = reader.result;                    

    }, false );

    if ( fileImage )
    {
        reader.readAsDataURL( fileImage );
    }

}

document.querySelector( "#imageID" ).addEventListener( "change", function() {

    previewImage( this, "#imagePreviewID", "#imageStringID" );

} )
/* Simple || */

<form>

    File Upload: <input type="file" id="imageID" /><br />
    Preview: <img src="#" id="imagePreviewID" /><br />    
    String base64: <textarea id="imageStringID" rows="10" cols="50"></textarea>

</form>

codesanbox

Answer 6

功能使用jquery将图像转换为base64（您可以转换为vanila js）。希望对你有帮助！

用法：input is your nameId input has file image

<input type="file" id="asd"/>
<button onclick="proccessData()">Submit</button>

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.5.1/jquery.min.js"></script>
<script>

async function converImageToBase64(inputId) {
  let image = $('#'+inputId)[0]['files']

  if (image && image[0]) {
    const reader = new FileReader();

    return new Promise(resolve => {
      reader.onload = ev => {
        resolve(ev.target.result)
      }
      reader.readAsDataURL(image[0])
    })
  }
}

async function proccessData() {
  const image = await converImageToBase64('asd')
  console.log(image)
}

</script>

示例：converImageToBase64('yourFileInputId')

https://codepen.io/mariohandsome/pen/yLadmVb

Answer 7

对于现代浏览器（不支持 IE）

HTML 文件输入

<style>
.upload-button {
  background-color: grey;
}

.upload-button input{
  display:none;
}
</style>
<label for="upload-photo" class="upload-button">
    Upload file
    <input
     type="file"
     id="upload-photo"
    </input>
</label>

JS

document.getElementById("upload-photo").addEventListener("change", function({target}){
 if (target.files && target.files.length) {
      try {
        const uploadedImageBase64 = await convertFileToBase64(target.files[0]); 
        //do something with above data string 
      } catch() {
        //handle error
      }
    }
})

function convertFileToBase64(file) {
  return new Promise((resolve, reject) => {
    const reader = new FileReader();
    reader.readAsDataURL(file);
    reader.onload = () => resolve(reader.result as string);
    reader.onerror = reject;
  });
}

图像转换为Base64

7 个答案:

对于现代浏览器（不支持 IE）