Javascript读取文件而不使用输入

由 et_qui发布于 2020-05-24 00:25:58

我有此代码，要将文件转换为base64，我必须单击“选择文件”，然后选择它。我想对文件名进行硬编码，以便在页面加载时将其转换为base64。

JavaScript：

var handleFileSelect = function(evt) {
  var files = evt.target.files;
  var file = files[0];

  if (files && file) {
    var reader = new FileReader();

    reader.onload = function(readerEvt) {
      var binaryString = readerEvt.target.result;
      document.getElementById("base64textarea").value = btoa(binaryString);
    };

    reader.readAsBinaryString(file);
  }

  if (window.File && window.FileReader
      && window.FileList && window.Blob) {
    document.getElementById('filePicker')
        .addEventListener('change', handleFileSelect, false);
  } else {
    alert('The File APIs are not fully supported in this browser.');
  }
};

HTML：

<div>
  <div>
    <label for="filePicker">Choose or drag a file:</label><br/>
    <input type="file" id="filePicker">
  </div>
  </br>
  <div>
    <h1>Base64 encoded version</h1>
    <textarea id="base64textarea"
        placeholder="Base64 will appear here"
        cols="50" rows="15">
    </textarea>
  </div>
</div>

编辑：谢谢您的回答，他们真的很有帮助。

所以狠在乎

2020-05-24 00:25:58

You can launch chromium, chrome browser with --allow-file-access-from-files flag set, use fetch() of XMLHttpRequest() to request file from local filesystem.

fetch("file:///path/to/file")
.then(response => response.arrayBuffer())
.then(ab => {
  // do stuff with `ArrayBuffer` representation of file
})
.catch(err => console.log(err));

See also Read local XML with JS

云淡，风清

2020-05-24 00:25:58

You simply can't do what you are trying to do. Setting the path for an input element through Javascript is not possible, as a security measure. Please check here: How to resolve the C:\fakepath?

院子里画沙

2020-05-24 00:25:58

File API不能在没有用户干预的情况下读取本地文件，但是Web API可以（当然，在其局限性之内，例如在不显式启用对本地文件的访问权限的情况下不能在Chromium中工作）。

因此，在这种情况下，如果有人需要一个有效的示例，说明如何在无需用户干预的情况下加载本地文件，即无需用户按下任何INPUT按钮（但仍为用户提供了中止加载的方式）。

参数：文件名，请求类型（文本，blob等），MIME类型以及文件完全加载后要执行的功能。文件被加载到变量X中，然后用于填充对象。

要中止文件读取，只需单击进度条（也只是一个示例，对于程序正常工作不是必需的）。因为它是异步的，所以可以同时读取所需数量的文件（为每个文件创建一个进度条）。

我只为文本文件和视频创建了示例，但它可以与任何类型的文件一起使用。

<html>
<head>
<meta charset="utf-8"/>
<script type="text/javascript">
function LoadFile(FileName,RespType,FileType,RunMe)
{   var AJAXFileReader=new XMLHttpRequest();

    // Creates new progress bar.
    var ProgressBar=CreateSVGProgBar("ProgressBars");

    AJAXFileReader.addEventListener("progress",
        function FRProgress(AJAXFREvt)
        {   // Calculate progress.
            var X=-1;

            if (AJAXFREvt.lengthComputable)
                X=Math.trunc(AJAXFREvt.loaded/AJAXFREvt.total*100);

            ShowProgressBar(ProgressBar,FileName,X);
        });

    AJAXFileReader.addEventListener("error",function FRFailed()
        {   // This will be executed if an error occurs.
            console.log("Error:",this.status);
        });

    AJAXFileReader.addEventListener("timeout",function FRTimeOut()
        {   // This will be executed if the reading times out.
            console.log("File reading timed out!");
        });

    AJAXFileReader.addEventListener("abort",
        function FRCancel()
        {   // This will confirm reading was aborted.
            console.log("File reading cancelled by user!");
        });

    ProgressBar.addEventListener("click",
        function KillMe()
        {   // Adds an abort command to the object.
            console.log(AJAXFileReader.readyState);
            if (AJAXFileReader.readyState!=4)
            {   console.log("Aborting file reading...");
                AJAXFileReader.abort();
            }
            ProgressBar.removeEventListener("click",KillMe);
        },
        false);

    AJAXFileReader.addEventListener("load",
        function Finished()
        {   // When reading is finished, send data to external function.
            if ((this.readyState==4)&&(this.status==200))
            {   ShowProgressBar(ProgressBar,FileName,100);
                RunMe(this.response);
                //ProgressBar.click();
            }
        },
        false);

    AJAXFileReader.open("GET",FileName,true);
    AJAXFileReader.overrideMimeType(FileType);
    AJAXFileReader.responseType=RespType;
    AJAXFileReader.timeout=10000; // Setting time-out to 10 s.

    AJAXFileReader.send();
}

function CreateSVGProgBar(AnchorId)
{   // Creates new SVG progress bar.
    var Parent=document.getElementById(AnchorId);
    var NewSVG=document.createElementNS("http://www.w3.org/2000/svg","svg");
    NewSVG.setAttribute("viewBox","0 0 102 22");
    NewSVG.setAttribute("width","102");
    NewSVG.setAttribute("height","22");
    Parent.appendChild(NewSVG);
    return NewSVG;
}

function ShowProgressBar(E,N,X)
{   // Show progress bar.
    var P=X<0?"???":X+"%";

    E.innerHTML="<text x=\"50\" y=\"16\" font-size=\"12\" fill=\"black\" stroke=\"black\" text-anchor=\"middle\">"+N+"</text><rect x=\"1\" y=\"1\" width=\""+X+"\" height=\"20\" fill=\""+(X<100?"#FF0000":"#0000FF")+"\" stroke=\"none\"/><rect x=\"1\" y=\"1\" width=\"100\" height=\"20\" fill=\"none\" stroke=\"black\" stroke-width=\"1\"/><text x=\""+X/2+"\" y=\"16\" font-size=\"12\" fill=\"black\" stroke=\"black\" text-anchor=\"middle\">"+P+"</text>";
}

function TracerOn(X)
{   // This will be executed after the file is completely loaded.
    document.getElementById("Tron").innerHTML=X;
}

function PlayIt(X)
{   // This will be executed after the file is completely loaded.
    var blob_uri=URL.createObjectURL(X);
    document.getElementById("MagicalBox").appendChild(document.createElement("source")).src=blob_uri;
}

function Startup()
{   // Run after the Page is loaded.
    LoadFile("example.txt","text","text/plain;charset=utf-8",TracerOn);
    LoadFile("video.mp4","blob","video/mp4",PlayIt);
}

</script>
</head>

<body onload="Startup()">

<div id="ProgressBars"></div>

<div id="Tron">Text...</div>

<video id="MagicalBox" width="400" controls>Video...</video>

</body>
</html>

et_qui

这家伙很懒，什么都没留下

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