TextEncoder
TextEncoder
takes a stream of code points as input and emits a stream of UTF-8 bytes.
Note: This feature is available in Web Workers.
Example
const encoder = new TextEncoder()
const view = encoder.encode('€')
console.log(view); // Uint8Array(3) [226, 130, 172]
Constructor
TextEncoder()
- Returns a newly constructed
TextEncoder
that will generate a byte stream with UTF-8 encoding.
Properties
The TextEncoder
interface doesn't inherit any property.
TextEncoder.prototype.encoding
Read only- Always returns "
utf-8
".
Methods
The TextEncoder
interface doesn't inherit any method.
TextEncoder.prototype.encode()
- Takes a
USVString
as input, and returns aUint8Array
containing UTF-8 encoded text. TextEncoder.prototype.encodeInto()
- Takes a
USVString
to encode and a destinationUint8Array
to put resulting UTF-8 encoded text into, and returns a dictionary object indicating the progress of the encoding. This is potentially more performant than the olderencode()
method.
Polyfill
The below polyfill is compliant with the standard and therefore only supports UTF-8. It is designed to work in IE5 "out of the box". However, in IE5-IE9, it will return a regular Array instead of a TypedArray. In those cases a polyfill might be impractical for large strings. Finally, note that you should run the below code through a minifier (especially closure compiler) to turn sequences like 0x1e << 3
into 0xf0
. These sequences are not already precomputed because they serve to aesthetically illustrate how the polyfill works.
if (typeof TextEncoder === "undefined") {
TextEncoder=function TextEncoder(){};
TextEncoder.prototype.encode = function encode(str) {
"use strict";
var Len = str.length, resPos = -1;
// The Uint8Array's length must be at least 3x the length of the string because an invalid UTF-16
// takes up the equivelent space of 3 UTF-8 characters to encode it properly. However, Array's
// have an auto expanding length and 1.5x should be just the right balance for most uses.
var resArr = typeof Uint8Array === "undefined" ? new Array(Len * 1.5) : new Uint8Array(Len * 3);
for (var point=0, nextcode=0, i = 0; i !== Len; ) {
point = str.charCodeAt(i), i += 1;
if (point >= 0xD800 && point <= 0xDBFF) {
if (i === Len) {
resArr[resPos += 1] = 0xef/*0b11101111*/; resArr[resPos += 1] = 0xbf/*0b10111111*/;
resArr[resPos += 1] = 0xbd/*0b10111101*/; break;
}
// https://mathiasbynens.be/notes/javascript-encoding#surrogate-formulae
nextcode = str.charCodeAt(i);
if (nextcode >= 0xDC00 && nextcode <= 0xDFFF) {
point = (point - 0xD800) * 0x400 + nextcode - 0xDC00 + 0x10000;
i += 1;
if (point > 0xffff) {
resArr[resPos += 1] = (0x1e/*0b11110*/<<3) | (point>>>18);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>12)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
continue;
}
} else {
resArr[resPos += 1] = 0xef/*0b11101111*/; resArr[resPos += 1] = 0xbf/*0b10111111*/;
resArr[resPos += 1] = 0xbd/*0b10111101*/; continue;
}
}
if (point <= 0x007f) {
resArr[resPos += 1] = (0x0/*0b0*/<<7) | point;
} else if (point <= 0x07ff) {
resArr[resPos += 1] = (0x6/*0b110*/<<5) | (point>>>6);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
} else {
resArr[resPos += 1] = (0xe/*0b1110*/<<4) | (point>>>12);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | ((point>>>6)&0x3f/*0b00111111*/);
resArr[resPos += 1] = (0x2/*0b10*/<<6) | (point&0x3f/*0b00111111*/);
}
}
if (typeof Uint8Array !== "undefined") return resArr.subarray(0, resPos + 1);
// else // IE 6-9
resArr.length = resPos + 1; // trim off extra weight
return resArr;
};
TextEncoder.prototype.toString = function(){return "[object TextEncoder]"};
try { // Object.defineProperty only works on DOM prototypes in IE8
Object.defineProperty(TextEncoder.prototype,"encoding",{
get:function(){if(TextEncoder.prototype.isPrototypeOf(this)) return"utf-8";
else throw TypeError("Illegal invocation");}
});
} catch(e) { /*IE6-8 fallback*/ TextEncoder.prototype.encoding = "utf-8"; }
if(typeof Symbol!=="undefined")TextEncoder.prototype[Symbol.toStringTag]="TextEncoder";
}
Source: https://github.com/anonyco/FastestSmallestTextEncoderDecoder
Specifications
Specification | Status | Comment |
---|---|---|
Encoding The definition of 'TextEncoder' in that specification. |
Living Standard | Initial definition. |
Browser compatibility
BCD tables only load in the browser
See also
- The
TextDecoder
interface describing the inverse operation. - Node.js supports global export from v11.0.0