Hướng dẫn can javascript access files?

I’m trying to implemennt a simple text file reader by creating a function that takes in the file’s path and converts each line of text into a char array, but it’s not working.

Nội dung chính

• Update 30/07/2018 (disclaimer):
• Update-2 (disclaimer):
• Modern solution:
• Local AJAX calls in Chrome are not supported due to same-origin-policy.
• Not the answer you're looking for? Browse other questions tagged javascript file-io xmlhttprequest or ask your own question.
• How do I read a .txt file in JavaScript?
• How do I open a file using JavaScript?
• How do we read and write files in JavaScript?
• Can JavaScript open a local file?

function readTextFile() {
  var rawFile = new XMLHttpRequest();
  rawFile.open("GET", "testing.txt", true);
  rawFile.onreadystatechange = function() {
    if (rawFile.readyState === 4) {
      var allText = rawFile.responseText;
      document.getElementById("textSection").innerHTML = allText;
    }
  }
  rawFile.send();
}

What is going wrong here?

This still doesn’t seem to work after changing the code a little bit from a previous revision and now it's giving me an XMLHttpRequest exception 101.

I’ve tested this on Firefox and it works, but in Google Chrome it just won't work and it keeps giving me an Exception 101. How can I get this to work on not just Firefox, but also on other browsers (especially Chrome)?

ggorlen

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asked Jan 21, 2013 at 20:14

3

You need to check for status 0 (as when loading files locally with XMLHttpRequest, you don't get a status returned because it's not from a Webserver)

function readTextFile(file)
{
    var rawFile = new XMLHttpRequest();
    rawFile.open("GET", file, false);
    rawFile.onreadystatechange = function ()
    {
        if(rawFile.readyState === 4)
        {
            if(rawFile.status === 200 || rawFile.status == 0)
            {
                var allText = rawFile.responseText;
                alert(allText);
            }
        }
    }
    rawFile.send(null);
}

And specify file:// in your filename:

readTextFile("file:///C:/your/path/to/file.txt");

Themroc

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answered Jan 21, 2013 at 20:20

Majid LaissiMajid Laissi

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29

After the introduction of fetch api in javascript, reading file contents could not be simpler.

reading a text file

fetch('file.txt')
  .then(response => response.text())
  .then(text => console.log(text))
  // outputs the content of the text file

reading a json file

fetch('file.json')
  .then(response => response.json())
  .then(jsonResponse => console.log(jsonResponse))     
   // outputs a javascript object from the parsed json

Update 30/07/2018 (disclaimer):

This technique works fine in Firefox, but it seems like Chrome's fetch implementation does not support file:/// URL scheme at the date of writing this update (tested in Chrome 68).

Update-2 (disclaimer):

This technique does not work with Firefox above version 68 (Jul 9, 2019) for the same (security) reason as Chrome: CORS request not HTTP. See https://developer.mozilla.org/en-US/docs/Web/HTTP/CORS/Errors/CORSRequestNotHttp.

OlivierM

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answered Sep 9, 2017 at 9:42

11

Visit Javascripture ! And go the section readAsText and try the example. You will be able to know how the readAsText function of FileReader works.

    
    
    
    
    
    

    

    ...
    
    
    

answered Mar 20, 2015 at 21:30

Amit ChaurasiaAmit Chaurasia

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3

var input = document.getElementById("myFile");
var output = document.getElementById("output");


input.addEventListener("change", function () {
  if (this.files && this.files[0]) {
    var myFile = this.files[0];
    var reader = new FileReader();
    
    reader.addEventListener('load', function (e) {
      output.textContent = e.target.result;
    });
    
    reader.readAsBinaryString(myFile);
  }   
});

answered Aug 22, 2017 at 10:46

3

Modern solution:

Use fileOrBlob.text() as follows:

When user uploads a text file via that input, it will be logged to the console. Here's a working jsbin demo.

Here's a more verbose version:

Currently (January 2020) this only works in Chrome and Firefox, check here for compatibility if you're reading this in the future: https://developer.mozilla.org/en-US/docs/Web/API/Blob/text

On older browsers, this should work:

Related: As of September 2020 the new Native File System API available in Chrome and Edge in case you want permanent read-access (and even write access) to the user-selected file.

2

Yes JS can read local files (see FileReader()) but not automatically: the user has to pass the file or a list of files to the script with an html .

Then with JS it is possible to process (example view) the file or the list of files, some of their properties and the file or files content.

What JS cannot do for security reasons is to access automatically (without the user input) to the filesystem of his computer.

To allow JS to access to the local fs automatically is needed to create not an html file with JS inside it but an hta document.

An hta file can contain JS or VBS inside it.

But the hta executable will work on windows systems only.

This is standard browser behavior.

Also Google Chrome worked at the fs API, more info here: http://www.html5rocks.com/en/tutorials/file/filesystem/

isherwood

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answered Jan 29, 2016 at 3:31

SparrowSparrow

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0

Using Fetch and async function

const logFileText = async file => {
    const response = await fetch(file)
    const text = await response.text()
    console.log(text)
}

logFileText('file.txt')

answered Jan 8, 2019 at 13:15

barro32barro32

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2

Try creating two functions:

function getData(){       //this will read file and send information to other function
       var xmlhttp;

       if (window.XMLHttpRequest) {
           xmlhttp = new XMLHttpRequest();               
       }           
       else {               
           xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");               
       }

       xmlhttp.onreadystatechange = function () {               
           if (xmlhttp.readyState == 4) {                   
             var lines = xmlhttp.responseText;    //*here we get all lines from text file*

             intoArray(lines);     *//here we call function with parameter "lines*"                   
           }               
       }

       xmlhttp.open("GET", "motsim1.txt", true);
       xmlhttp.send();    
}

function intoArray (lines) {
   // splitting all text data into array "\n" is splitting data from each new line
   //and saving each new line as each element*

   var lineArr = lines.split('\n'); 

   //just to check if it works output lineArr[index] as below
   document.write(lineArr[2]);         
   document.write(lineArr[3]);
}

Bill Bell

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answered Oct 16, 2013 at 23:29

1

Provably you already try it, type "false" as follows:

 rawFile.open("GET", file, false);

A-Sharabiani

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answered Nov 26, 2013 at 12:17

momenmomen

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other example - my reader with FileReader class

    
        
        
        
    
    
        
        
        

            
            
        
        Source file
    

answered Feb 19, 2015 at 15:35

webskywebsky

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1

This might help,

    var xmlhttp = window.XMLHttpRequest ? new XMLHttpRequest() : new ActiveXObject("Microsoft.XMLHTTP");

    xmlhttp.onreadystatechange = function () {
        if (xmlhttp.readyState == 4 && xmlhttp.status == 200) {
            alert(xmlhttp.responseText);
        }
    }

    xmlhttp.open("GET", "sample.txt", true);
    xmlhttp.send();

answered Nov 18, 2016 at 15:20

Sameera R.Sameera R.

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Local AJAX calls in Chrome are not supported due to same-origin-policy.

Error message on chrome is like this: "Cross origin requests are not supported for protocol schemes: http, data, chrome, chrome-extension, https."

This means that chrome creates a virtual disk for every domain to keep the files served by the domain using http/https protocols. Any access to files outside this virtual disk are restricted under same origin policy. AJAX requests and responses happen on http/https, therefore wont work for local files.

Firefox does not put such restriction, therefore your code will work happily on the Firefox. However there are workarounds for chrome too : see here.

answered Dec 26, 2018 at 12:12

1

Adding to some the above answers, this modified solution worked for me.

....

let fileInput  = document.getElementById('file-upload-input');
let files = fileInput.files;

//Use createObjectURL, this should address any CORS issues.
let filePath = URL.createObjectURL(files[0]);

....

function readTextFile(filePath){
    var rawFile = new XMLHttpRequest();
    rawFile.open("GET", filePath , true);
    rawFile.send(null);

    rawFile.onreadystatechange = function (){
        if(rawFile.readyState === 4){
            if(rawFile.status === 200 || rawFile.status == 0){
                var allText = rawFile.responseText;
                console.log(allText);
            }
        }
    }     
}

answered Dec 31, 2018 at 19:50

FabiiFabii

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function readTextFile(file) {
    var rawFile = new XMLHttpRequest(); // XMLHttpRequest (often abbreviated as XHR) is a browser object accessible in JavaScript that provides data in XML, JSON, but also HTML format, or even a simple text using HTTP requests.
    rawFile.open("GET", file, false); // open with method GET the file with the link file ,  false (synchronous)
    rawFile.onreadystatechange = function ()
    {
        if(rawFile.readyState === 4) // readyState = 4: request finished and response is ready
        {
            if(rawFile.status === 200) // status 200: "OK"
            {
                var allText = rawFile.responseText; //  Returns the response data as a string
                console.log(allText); // display text on the console
            }
        }
    }
    rawFile.send(null); //Sends the request to the server Used for GET requests with param null
}

readTextFile("text.txt"); //<= Call function ===== don't need "file:///..." just the path 

- read file text from javascript
- Console log text from file using javascript
- Google chrome and mozilla firefox

in my case i have this structure of files :

the console.log result :

answered Jan 18, 2019 at 9:38

nadir hamidounadir hamidou

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1

If you want to prompt the user to select a file, then read its contents:

// read the contents of a file input
const readInputFile = (inputElement, callback) => {
  const reader = new FileReader();
  reader.onload = () => {
    callback(reader.result)
  };
  reader.readAsText(inputElement.files[0]);
};
// create a file input and destroy it after reading it
const openFile = (callback) => {
  var el = document.createElement('input');
  el.setAttribute('type', 'file');
  el.style.display = 'none';
  document.body.appendChild(el);
  el.onchange = () => {readInputFile(el, (data) => {
    callback(data)
    document.body.removeChild(el);
  })}
  el.click();
}

Usage:

// prompt the user to select a file and read it
openFile(data => {
    console.log(data)
  })

answered Dec 16, 2020 at 15:13

yayayaya

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         Select All
        
    

answered Feb 22, 2018 at 7:41

Get local file data in js(data.js) load:

function loadMyFile(){
    console.log("ut:"+unixTimeSec());
    loadScript("data.js?"+unixTimeSec(), loadParse);
}
function loadParse(){
    var mA_=mSdata.split("\n");
    console.log(mA_.length);
}
function loadScript(url, callback){

    var script = document.createElement("script")
    script.type = "text/javascript";

    if (script.readyState){  //IE
        script.onreadystatechange = function(){
            if (script.readyState == "loaded" ||
                    script.readyState == "complete"){
                script.onreadystatechange = null;
                callback();
            }
        };
    } else {  //Others
        script.onload = function(){
            callback();
        };
    }

    script.src = url;
    document.getElementsByTagName("head")[0].appendChild(script);
}
function hereDoc(f) {
  return f.toString().
      replace(/^[^\/]+\/\*![^\r\n]*[\r\n]*/, "").
      replace(/[\r\n][^\r\n]*\*\/[^\/]+$/, "");
}
function unixTimeSec(){
    return Math.round( (new Date()).getTime()/1000);
}

file of data.js like:

var mSdata = hereDoc(function() {/*!
17,399
1237,399
BLAHBLAH
BLAHBLAH
155,82
194,376
*/});

dynamic unixTime queryString prevents cached.

AJ works in web http://.

answered Apr 26, 2019 at 5:20

1

How to read a local file?

By using this you will load a file by loadText() then JS will asynchronously wait until the file is read and loaded after that it will execture readText() function allowing you to continue with your normal JS logic (you can also write a try catch block on the loadText() function in the case any error arises) but for this example I keep it at minimal.

async function loadText(url) {
    text = await fetch(url);
    //awaits for text.text() prop 
    //and then sends it to readText()
    readText(await text.text());
}

function readText(text){
    //here you can continue with your JS normal logic
    console.log(text);
}

loadText('test.txt');

answered Oct 3, 2019 at 13:33

D.SnapD.Snap

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1

This function made for browsers and open file picker dialog and after user selection read file as binary and call callback function with read data:

function pickAndReadFile(callback) {
    var el = document.createElement('input');
    el.setAttribute('type', 'file');
    el.style.display = 'none';
    document.body.appendChild(el);
    el.onchange = function (){
        const reader = new FileReader();
        reader.onload = function () {
            callback(reader.result);
            document.body.removeChild(el);
        };
        reader.readAsBinaryString(el.files[0]);
    }
    el.click();
}

And use it like this:

pickAndReadFile(data => {
  console.log(data)
})

answered Dec 19, 2021 at 8:24

MSSMSS

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1

You can import my library:

then, the function fetchfile(path) will return the uploaded file

Please note: on Google Chrome if the HTML code is local, errors will appear, but saving the HTML code and the files online then running the online HTML file works.

answered Jan 3, 2019 at 23:40

In order to read a local file text through JavaScript using chrome, the chrome browser should run with the argument --allow-file-access-from-files to allow JavaScript to access local file, then you can read it using XmlHttpRequest like the following:

var xmlhttp = new XMLHttpRequest();
xmlhttp.onreadystatechange = function () {
   if (xmlhttp.readyState == 4) {
       var allText = xmlhttp.responseText;          
            }
        };
xmlhttp.open("GET", file, false);
xmlhttp.send(null);

answered Jan 7, 2019 at 9:56

Ali Ezzat OdehAli Ezzat Odeh

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I know, I am late at this party. Let me show you what I have got.

This is a simple reading of text file

var path = "C:\\path\\filename.txt"
var fs = require('fs')
fs.readFile(path , 'utf8', function(err, data) {
  if (err) throw err;
  console.log('OK: ' + filename);
  console.log(data)
});

I hope this helps.

answered Mar 16, 2020 at 9:50

1

Not the answer you're looking for? Browse other questions tagged javascript file-io xmlhttprequest or ask your own question.

How do I read a .txt file in JavaScript?

Use the fs. readFileSync() method to read a text file into an array in JavaScript, e.g. const contents = readFileSync(filename, 'utf-8'). split('\n') . The method will return the contents of the file, which we can split on each newline character to get an array of strings.

How do I open a file using JavaScript?

How to Open a File in Javascript.

Right-click the HTML file you want to use to open the file. Click "Open With," then double-click the preferred JavaScript editor. ... .

Create the JavaScript function. ... .

Add the function to the "Browse" button on the Web page. ... .

Save the file and open it in your default Web browser..

How do we read and write files in JavaScript?

How to read and write a file using javascript?.

file=fopen(getScriptPath(),0); The function fread() is used for reading the file content..

str = fread(file,flength(file) ; The function fwrite() is used to write the contents to the file..

file = fopen("c:\MyFile.txt", 3);// opens the file for writing..

Can JavaScript open a local file?

JavaScript cannot typically access local files in new browsers, but the XMLHttpRequest object can be used to read files. So it is actually Ajax (and not Javascript) which is reading the file.