如何在JavaScript中读取文本文件

韩飞翮

2023-03-14

问题内容：

我试图将文本文件加载到我的JavaScript文件中，然后从该文件中读取行以获取信息，我尝试使用FileReader，但它似乎无法正常工作。有人可以帮忙吗？

function analyze(){
   var f = new FileReader();

   f.onloadend = function(){
       console.log("success");
   }
   f.readAsText("cities.txt");
}

问题答案：

是的，可以使用FileReader，我已经做了一个示例，这是代码：

<!DOCTYPE html>
<html>
  <head>
    <title>Read File (via User Input selection)</title>
    <script type="text/javascript">
    var reader; //GLOBAL File Reader object for demo purpose only

    /**
     * Check for the various File API support.
     */
    function checkFileAPI() {
        if (window.File && window.FileReader && window.FileList && window.Blob) {
            reader = new FileReader();
            return true; 
        } else {
            alert('The File APIs are not fully supported by your browser. Fallback required.');
            return false;
        }
    }

    /**
     * read text input
     */
    function readText(filePath) {
        var output = ""; //placeholder for text output
        if(filePath.files && filePath.files[0]) {           
            reader.onload = function (e) {
                output = e.target.result;
                displayContents(output);
            };//end onload()
            reader.readAsText(filePath.files[0]);
        }//end if html5 filelist support
        else if(ActiveXObject && filePath) { //fallback to IE 6-8 support via ActiveX
            try {
                reader = new ActiveXObject("Scripting.FileSystemObject");
                var file = reader.OpenTextFile(filePath, 1); //ActiveX File Object
                output = file.ReadAll(); //text contents of file
                file.Close(); //close file "input stream"
                displayContents(output);
            } catch (e) {
                if (e.number == -2146827859) {
                    alert('Unable to access local files due to browser security settings. ' + 
                     'To overcome this, go to Tools->Internet Options->Security->Custom Level. ' + 
                     'Find the setting for "Initialize and script ActiveX controls not marked as safe" and change it to "Enable" or "Prompt"'); 
                }
            }       
        }
        else { //this is where you could fallback to Java Applet, Flash or similar
            return false;
        }       
        return true;
    }

    /**
     * display content using a basic HTML replacement
     */
    function displayContents(txt) {
        var el = document.getElementById('main'); 
        el.innerHTML = txt; //display output in DOM
    }   
</script>
</head>
<body onload="checkFileAPI();">
    <div id="container">    
        <input type="file" onchange='readText(this)' />
        <br/>
        <hr/>   
        <h3>Contents of the Text file:</h3>
        <div id="main">
            ...
        </div>
    </div>
</body>
</html>

最后，我只是读了其他一些吸引我的答案，但正如他们所建议的那样，您可能正在寻找使您能够从JavaScript文件所在的服务器（或设备）加载文本文件的代码。如果是这种情况，那么您希望AJAX代码动态加载文档，如下所示：

<!DOCTYPE html>
<html>
<head><meta charset="utf-8" />
<title>Read File (via AJAX)</title>
<script type="text/javascript">
var reader = new XMLHttpRequest() || new ActiveXObject('MSXML2.XMLHTTP');

function loadFile() {
    reader.open('get', 'test.txt', true); 
    reader.onreadystatechange = displayContents;
    reader.send(null);
}

function displayContents() {
    if(reader.readyState==4) {
        var el = document.getElementById('main');
        el.innerHTML = reader.responseText;
    }
}

</script>
</head>
<body>
<div id="container">
    <input type="button" value="test.txt"  onclick="loadFile()" />
    <div id="main">
    </div>
</div>
</body>
</html>

如何在JavaScript中读取文本文件

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