Decode UTF-8 with Javascript

I have Javascript in an XHTML web page that is passing UTF-8 encoded strings. It needs to continue to pass the UTF-8 version, as well as decode it. How is it possible to decode a UTF-8 string for display?

<script type="text/javascript">
// <![CDATA[
function updateUser(usernameSent){
    var usernameReceived = usernameSent; // Current value: Größe
    var usernameDecoded = usernameReceived;  // Decode to: Größe
    var html2id = '';
    html2id += 'Encoded: ' + usernameReceived + '<br />Decoded: ' + usernameDecoded;
    document.getElementById('userId').innerHTML = html2id;
}
// ]]>
</script>

To answer the original question: here is how you decode utf-8 in javascript:

http://ecmanaut.blogspot.ca/2006/07/encoding-decoding-utf8-in-javascript.html

Specifically,

function encode_utf8(s) {
  return unescape(encodeURIComponent(s));
}

function decode_utf8(s) {
  return decodeURIComponent(escape(s));
}

We have been using this in our production code for 6 years, and it has worked flawlessly.

Note, however, that escape() and unescape() are deprecated. See this.

This should work:

// http://www.onicos.com/staff/iz/amuse/javascript/expert/utf.txt

/* utf.js - UTF-8 <=> UTF-16 convertion
 *
 * Copyright (C) 1999 Masanao Izumo <iz@onicos.co.jp>
 * Version: 1.0
 * LastModified: Dec 25 1999
 * This library is free.  You can redistribute it and/or modify it.
 */

function Utf8ArrayToStr(array) {
    var out, i, len, c;
    var char2, char3;

    out = "";
    len = array.length;
    i = 0;
    while(i < len) {
	c = array[i++];
	switch(c >> 4)
	{ 
	  case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
	    // 0xxxxxxx
	    out += String.fromCharCode(c);
	    break;
	  case 12: case 13:
	    // 110x xxxx   10xx xxxx
	    char2 = array[i++];
	    out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
	    break;
	  case 14:
	    // 1110 xxxx  10xx xxxx  10xx xxxx
        char2 = array[i++];
	    char3 = array[i++];
	    out += String.fromCharCode(((c & 0x0F) << 12) |
					   ((char2 & 0x3F) << 6) |
					   ((char3 & 0x3F) << 0));
	    break;
	}
    }

    return out;
}

Check out the JSFiddle demo.

Also see the related questions: here and here

Perhaps using the textDecoder will be sufficient.

Not supported in IE though.

var decoder = new TextDecoder('utf-8'),
    decodedMessage;

decodedMessage = decoder.decode(message.data);

Handling non-UTF8 text

In this example, we decode the Russian text "Привет, мир!", which means "Hello, world." In our TextDecoder() constructor, we specify the Windows-1251 character encoding, which is appropriate for Cyrillic script.

    let win1251decoder = new TextDecoder('windows-1251');
    let bytes = new Uint8Array([207, 240, 232, 226, 229, 242, 44, 32, 236, 232, 240, 33]);
    console.log(win1251decoder.decode(bytes)); // Привет, мир!

The interface for the TextDecoder is described here.

Retrieving a byte array from a string is equally simpel:

const decoder = new TextDecoder();
const encoder = new TextEncoder();

const byteArray = encoder.encode('Größe');
// converted it to a byte array

// now we can decode it back to a string if desired
console.log(decoder.decode(byteArray));

If you have it in a different encoding then you must compensate for that upon encoding. The parameter in the constructor for the TextEncoder is any one of the valid encodings listed here.

Update @Albert's answer adding condition for emoji.

function Utf8ArrayToStr(array) {
    var out, i, len, c;
    var char2, char3, char4;

    out = "";
    len = array.length;
    i = 0;
    while(i < len) {
    c = array[i++];
    switch(c >> 4)
    { 
      case 0: case 1: case 2: case 3: case 4: case 5: case 6: case 7:
        // 0xxxxxxx
        out += String.fromCharCode(c);
        break;
      case 12: case 13:
        // 110x xxxx   10xx xxxx
        char2 = array[i++];
        out += String.fromCharCode(((c & 0x1F) << 6) | (char2 & 0x3F));
        break;
      case 14:
        // 1110 xxxx  10xx xxxx  10xx xxxx
        char2 = array[i++];
        char3 = array[i++];
        out += String.fromCharCode(((c & 0x0F) << 12) |
                       ((char2 & 0x3F) << 6) |
                       ((char3 & 0x3F) << 0));
        break;
     case 15:
        // 1111 0xxx 10xx xxxx 10xx xxxx 10xx xxxx
        char2 = array[i++];
        char3 = array[i++];
        char4 = array[i++];
        out += String.fromCodePoint(((c & 0x07) << 18) | ((char2 & 0x3F) << 12) | ((char3 & 0x3F) << 6) | (char4 & 0x3F));

        break;
    }

    return out;
}

Here is a solution handling all Unicode code points include upper (4 byte) values and supported by all modern browsers (IE and others > 5.5). It uses decodeURIComponent(), but NOT the deprecated escape/unescape functions:

function utf8_to_str(a) {
    for(var i=0, s=''; i<a.length; i++) {
        var h = a[i].toString(16)
        if(h.length < 2) h = '0' + h
        s += '%' + h
    }
    return decodeURIComponent(s)
}

Tested and available on GitHub

To create UTF-8 from a string:

function utf8_from_str(s) {
    for(var i=0, enc = encodeURIComponent(s), a = []; i < enc.length;) {
        if(enc[i] === '%') {
            a.push(parseInt(enc.substr(i+1, 2), 16))
            i += 3
        } else {
            a.push(enc.charCodeAt(i++))
        }
    }
    return a
}

Tested and available on GitHub

@albert's solution was the closest I think but it can only parse up to 3 byte utf-8 characters

function utf8ArrayToStr(array) {
  var out, i, len, c;
  var char2, char3;

  out = "";
  len = array.length;
  i = 0;

  // XXX: Invalid bytes are ignored
  while(i < len) {
    c = array[i++];
    if (c >> 7 == 0) {
      // 0xxx xxxx
      out += String.fromCharCode(c);
      continue;
    }

    // Invalid starting byte
    if (c >> 6 == 0x02) {
      continue;
    }

    // #### MULTIBYTE ####
    // How many bytes left for thus character?
    var extraLength = null;
    if (c >> 5 == 0x06) {
      extraLength = 1;
    } else if (c >> 4 == 0x0e) {
      extraLength = 2;
    } else if (c >> 3 == 0x1e) {
      extraLength = 3;
    } else if (c >> 2 == 0x3e) {
      extraLength = 4;
    } else if (c >> 1 == 0x7e) {
      extraLength = 5;
    } else {
      continue;
    }

    // Do we have enough bytes in our data?
    if (i+extraLength > len) {
      var leftovers = array.slice(i-1);

      // If there is an invalid byte in the leftovers we might want to
      // continue from there.
      for (; i < len; i++) if (array[i] >> 6 != 0x02) break;
      if (i != len) continue;

      // All leftover bytes are valid.
      return {result: out, leftovers: leftovers};
    }
    // Remove the UTF-8 prefix from the char (res)
    var mask = (1 << (8 - extraLength - 1)) - 1,
        res = c & mask, nextChar, count;

    for (count = 0; count < extraLength; count++) {
      nextChar = array[i++];

      // Is the char valid multibyte part?
      if (nextChar >> 6 != 0x02) {break;};
      res = (res << 6) | (nextChar & 0x3f);
    }

    if (count != extraLength) {
      i--;
      continue;
    }

    if (res <= 0xffff) {
      out += String.fromCharCode(res);
      continue;
    }

    res -= 0x10000;
    var high = ((res >> 10) & 0x3ff) + 0xd800,
        low = (res & 0x3ff) + 0xdc00;
    out += String.fromCharCode(high, low);
  }

  return {result: out, leftovers: []};
}

This returns {result: "parsed string", leftovers: [list of invalid bytes at the end]} in case you are parsing the string in chunks.

EDIT: fixed the issue that @unhammer found.

// String to Utf8 ByteBuffer

function strToUTF8(str){
  return Uint8Array.from(encodeURIComponent(str).replace(/%(..)/g,(m,v)=>{return String.fromCodePoint(parseInt(v,16))}), c=>c.codePointAt(0))
}

// Utf8 ByteArray to string

function UTF8toStr(ba){
  return decodeURIComponent(ba.reduce((p,c)=>{return p+'%'+c.toString(16),''}))
}

This is what I found after a more specific Google search than just UTF-8 encode/decode. so for those who are looking for a converting library to convert between encodings, here you go.

https://github.com/inexorabletash/text-encoding

var uint8array = new TextEncoder().encode(str);
var str = new TextDecoder(encoding).decode(uint8array);

Paste from repo readme

All encodings from the Encoding specification are supported:

utf-8 ibm866 iso-8859-2 iso-8859-3 iso-8859-4 iso-8859-5 iso-8859-6 iso-8859-7 iso-8859-8 iso-8859-8-i iso-8859-10 iso-8859-13 iso-8859-14 iso-8859-15 iso-8859-16 koi8-r koi8-u macintosh windows-874 windows-1250 windows-1251 windows-1252 windows-1253 windows-1254 windows-1255 windows-1256 windows-1257 windows-1258 x-mac-cyrillic gb18030 hz-gb-2312 big5 euc-jp iso-2022-jp shift_jis euc-kr replacement utf-16be utf-16le x-user-defined

(Some encodings may be supported under other names, e.g. ascii, iso-8859-1, etc. See Encoding for additional labels for each encoding.)

Using my 1.6KB library, you can do

ToString(FromUTF8(Array.from(usernameReceived)))

You should take decodeURI for it.

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/decodeURI

As simple as this:

decodeURI('https://developer.mozilla.org/ru/docs/JavaScript_%D1%88%D0%B5%D0%BB%D0%BB%D1%8B');
// "https://developer.mozilla.org/ru/docs/JavaScript_шеллы"

Consider to use it inside try catch block for not missing an URIError.

Also it has full browsers support.

I reckon the easiest way would be to use a built-in js functions decodeURI() / encodeURI().

function (usernameSent) {
  var usernameEncoded = usernameSent; // Current value: utf8
  var usernameDecoded = decodeURI(usernameReceived);  // Decoded
  // do stuff
}

This is a solution with extensive error reporting.

It would take an UTF-8 encoded byte array (where byte array is represented as array of numbers and each number is an integer between 0 and 255 inclusive) and will produce a JavaScript string of Unicode characters.

function getNextByte(value, startByteIndex, startBitsStr, 
                     additional, index) 
{
    if (index >= value.length) {
        var startByte = value[startByteIndex];
        throw new Error("Invalid UTF-8 sequence. Byte " + startByteIndex 
            + " with value " + startByte + " (" + String.fromCharCode(startByte) 
            + "; binary: " + toBinary(startByte)
            + ") starts with " + startBitsStr + " in binary and thus requires " 
            + additional + " bytes after it, but we only have " 
            + (value.length - startByteIndex) + ".");
    }
    var byteValue = value[index];
    checkNextByteFormat(value, startByteIndex, startBitsStr, additional, index);
    return byteValue;
}

function checkNextByteFormat(value, startByteIndex, startBitsStr, 
                             additional, index) 
{
    if ((value[index] & 0xC0) != 0x80) {
        var startByte = value[startByteIndex];
        var wrongByte = value[index];
        throw new Error("Invalid UTF-8 byte sequence. Byte " + startByteIndex 
             + " with value " + startByte + " (" +String.fromCharCode(startByte) 
             + "; binary: " + toBinary(startByte) + ") starts with " 
             + startBitsStr + " in binary and thus requires " + additional 
             + " additional bytes, each of which shouls start with 10 in binary."
             + " However byte " + (index - startByteIndex) 
             + " after it with value " + wrongByte + " (" 
             + String.fromCharCode(wrongByte) + "; binary: " + toBinary(wrongByte)
             +") does not start with 10 in binary.");
    }
}

function fromUtf8 (str) {
        var value = [];
        var destIndex = 0;
        for (var index = 0; index < str.length; index++) {
            var code = str.charCodeAt(index);
            if (code <= 0x7F) {
                value[destIndex++] = code;
            } else if (code <= 0x7FF) {
                value[destIndex++] = ((code >> 6 ) & 0x1F) | 0xC0;
                value[destIndex++] = ((code >> 0 ) & 0x3F) | 0x80;
            } else if (code <= 0xFFFF) {
                value[destIndex++] = ((code >> 12) & 0x0F) | 0xE0;
                value[destIndex++] = ((code >> 6 ) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 0 ) & 0x3F) | 0x80;
            } else if (code <= 0x1FFFFF) {
                value[destIndex++] = ((code >> 18) & 0x07) | 0xF0;
                value[destIndex++] = ((code >> 12) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 6 ) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 0 ) & 0x3F) | 0x80;
            } else if (code <= 0x03FFFFFF) {
                value[destIndex++] = ((code >> 24) & 0x03) | 0xF0;
                value[destIndex++] = ((code >> 18) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 12) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 6 ) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 0 ) & 0x3F) | 0x80;
            } else if (code <= 0x7FFFFFFF) {
                value[destIndex++] = ((code >> 30) & 0x01) | 0xFC;
                value[destIndex++] = ((code >> 24) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 18) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 12) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 6 ) & 0x3F) | 0x80;
                value[destIndex++] = ((code >> 0 ) & 0x3F) | 0x80;
            } else {
                throw new Error("Unsupported Unicode character \"" 
                    + str.charAt(index) + "\" with code " + code + " (binary: " 
                    + toBinary(code) + ") at index " + index
                    + ". Cannot represent it as UTF-8 byte sequence.");
            }
        }
        return value;
    }

const decoder = new TextDecoder();
console.log(decoder.decode(new Uint8Array([97])));

MDN resource link

I searched for a simple solution and this works well for me:

//input data
view = new Uint8Array(data);

//output string
serialString = ua2text(view);

//convert UTF8 to string
function ua2text(ua) {
    s = "";
    for (var i = 0; i < ua.length; i++) {
        s += String.fromCharCode(ua[i]);
    }
    return s;				
}

Only issue I have is sometimes I get one character at a time. This might be by design with my source of the arraybuffer. I'm using https://github.com/xseignard/cordovarduino to read serial data on an android device.

Preferably, as others have suggested, use the Encoding API. But if you need to support IE (for some strange reason) MDN recommends this repo FastestSmallestTextEncoderDecoder

If you need to make use of the polyfill library:

    import {encode, decode} from "fastestsmallesttextencoderdecoder";

Then (regardless of the polyfill) for encoding and decoding:

    // takes in USVString and returns a Uint8Array object
    const encoded = new TextEncoder().encode('€')
    console.log(encoded);

    // takes in an ArrayBuffer or an ArrayBufferView and returns a DOMString
    const decoded = new TextDecoder().decode(encoded);
    console.log(decoded);