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This is an experimental technology
Check the Browser compatibility table carefully before using this in production.

TextEncoder takes a stream of code points as input and emits a stream of bytes. For a more scalable, non-native library, see StringView – a C-like representation of strings based on typed arrays.

Note: Firefox, Chrome and Opera used to have support for encoding types other than utf-8 (such as utf-16iso-8859-2, koi8, cp1261, and gbk). As of Firefox 48 (ticket), Chrome 54 (ticket) and Opera 41, no other encoding types are available other than utf-8, in order to match the spec. In all cases, passing in an encoding type to the constructor will be ignored and a utf-8 TextEncoder will be created (the TextDecoder still allows for other decoding types). 

Note: There is a polyfill implementation to support all the legacy encodings in GitHub.

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.encoding Read only
Is a DOMString containing the name of the encoder, that is a string describing the method the TextEncoder will use.

Methods

The TextEncoder interface doesn't inherit any method.

TextEncoder.encode()
Returns a Uint8Array containing utf-8 encoded text.

 

Polyfill

The below polyfill will only furfill the specs demanded by the W3 (no character encodings other than UTF-8 supported, unfourtunately ☹️). 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 such circumstances as these with such memory inefficient slow browsers, this polyfill (or any polyfill for that matter) would be impractical for large strings in such old browsers. Finally, note that 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;
        var resArr = typeof Uint8Array === "undefined" ? new Array(Len * 2) : 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 new Uint8Array(resArr.buffer.slice(0, resPos+1));
        else return resArr.length === resPos+1 ? resArr : resArr.slice(0, resPos+1); // IE 6-9
    };
    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";
}

Specifications

Specification Status Comment
Encoding
The definition of 'TextEncoder' in that specification.
Living Standard Initial definition.

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support38 ?

19

181

No25 No
Available in Web Workers38 ?20 No25 No
TextEncoder() constructor

532

38 — 533

?

484

38 — 485

19 — 386

181

No25 No
encoding38 ?

19

181

No25 No
encode38 ?

19

181

No25 No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support3838 ?

19

181

? No ?
Available in Web Workers3838 ?20 ? No ?
TextEncoder() constructor3838 ?

484

38 — 485

19 — 386

181

? No ?
encoding3838 ?

19

181

? No ?
encode3838 ?

19

181

? No ?

1. Firefox 18 implemented an earlier and slightly different version of the specification.

2. Does not accept parameters. Supports only utf-8 encoding.

3. Throws RangeError exception for unknown encoding types.

4. The constructor accepts an encoding type label argument, but the value is ignored. Only utf-8 encoding is supported.

5. If the encoding type label argument is invalid, then a RangeError exception is thrown.

6. If the encoding type label argument is invalid, then a TypeError exception is thrown.

See also

文件標籤與貢獻者

最近更新: anonyco,