如何将 Base64 字符串转换为 javascript 文件对象，如文件输入表单?

2022-01-21 00:00:00 file base64 forms javascript html

我想将从文件中提取的 Base64String(例如:AAAAA....~")转换为 javascript 文件对象.

I want to convert Base64String extracted from file(ex: "AAAAA....~") to a javascript file object.

我的意思的javascript文件对象是这样的代码:

The javascript file object what I mean is like this code:

HTML:

<input type="file" id="selectFile" >

JS:

$('#selectFile').on('change', function(e) {
  var file = e.target.files[0];

  console.log(file)
}

'file' 变量是一个 javascript 文件对象.所以我想像这样将base64字符串转换为javascript文件对象.

'file' variable is a javascript file object. So I want to convert a base64 string to the javascript file object like that.

我只想通过解码base64字符串(由其他应用程序从文件中编码)来获取文件对象，而不需要html文件输入表单.

I just want to get file object by decoding base64 string (encoded by other app from a file) without html file input form.

谢谢.

推荐答案

方式一:只适用于dataURL，不适用于其他类型的url.

Way 1: only works for dataURL, not for other types of url.

 function dataURLtoFile(dataurl, filename) {
 
        var arr = dataurl.split(','),
            mime = arr[0].match(/:(.*?);/)[1],
            bstr = atob(arr[1]), 
            n = bstr.length, 
            u8arr = new Uint8Array(n);
            
        while(n--){
            u8arr[n] = bstr.charCodeAt(n);
        }
        
        return new File([u8arr], filename, {type:mime});
    }
    
    //Usage example:
    var file = dataURLtoFile('data:text/plain;base64,aGVsbG8gd29ybGQ=','hello.txt');
    console.log(file);

方式 2: 适用于任何类型的 url，(http url、dataURL、blobURL 等...)

Way 2: works for any type of url, (http url, dataURL, blobURL, etc...)

 //return a promise that resolves with a File instance
    function urltoFile(url, filename, mimeType){
        return (fetch(url)
            .then(function(res){return res.arrayBuffer();})
            .then(function(buf){return new File([buf], filename,{type:mimeType});})
        );
    }
    
    //Usage example:
    urltoFile('data:text/plain;base64,aGVsbG8gd29ybGQ=', 'hello.txt','text/plain')
    .then(function(file){ console.log(file);});

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