Run results for: TextDecoder

Run details:

User agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:85.0) Gecko/20100101 Firefox/85.0

Browser: Firefox 85

Operating system: Windows 7

Device Platform: Desktop

Date tested: 3 years ago

Test name	Executions per second
TextDecoder	2698469.5 Ops/sec
Concat	2495531.5 Ops/sec

Script Preparation code:

var ToStringFromUTF16_1 = (function() {
            var UTF16 = new TextDecoder("utf-16");
            return function(bytes, startIndex, length) {
                startIndex = startIndex | 0;
                if (typeof length !== "undefined") length += startIndex;
                return UTF16.decode(bytes.subarray(startIndex, length));
            };
    })();

var ToStringFromUTF16_2 = (function() {
            var fromCharCode = String.fromCharCode;
            return function (bytes, startIndex, length) {
                startIndex = startIndex | 0;
                if (typeof length === "undefined")
                    length = bytes.length - startIndex;
                var s = "",
                    endIndex = startIndex + length,
                    i = startIndex;
                while (i < endIndex) {
                    var octet = bytes[i],
                        bytesNeeded = 0,
                        codePoint = 0;
                    if (octet <= 0x7F) {
                        bytesNeeded = 0;
                        codePoint = octet & 0xFF;
                    } else if (octet <= 0xDF) {
                        bytesNeeded = 1;
                        codePoint = octet & 0x1F;
                    } else if (octet <= 0xEF) {
                        bytesNeeded = 2;
                        codePoint = octet & 0x0F;
                    } else if (octet <= 0xF4) {
                        bytesNeeded = 3;
                        codePoint = octet & 0x07;
                    }
                    if (endIndex - i - bytesNeeded > 0) {
                        for (var j = 0; j < bytesNeeded; j++) {
                          octet = bytes[i + j + 1];
                          codePoint = (codePoint << 6) | (octet & 0x3F);
                        }
                    } else {
                        codePoint = 0xFFFD; // REPLACEMENT CHARACTER
                        bytesNeeded = endIndex - i;
                    }
                    //s += String.fromCodePoint(codePoint);                   
                    //if (!(codePoint < 0x10FFFF && (codePoint>>>0) === codePoint))
                    //    throw RangeError("Invalid code point: " + codePoint);
                    if (codePoint <= 0xFFFF) { // BMP code point
                        s += fromCharCode(codePoint);
                    } else {
                        codePoint -= 0x10000;
                        s += fromCharCode((codePoint >> 10) + 0xD800,    // high surrogate
                                          (codePoint % 0x400) + 0xDC00); // low surrogate
                    }
                    i += bytesNeeded + 1;
                }
                return s;
            };
    })();

var bytes = new Uint8Array([32, 0, 32, 0, 32, 0, 32, 0, 32, 0, 32, 0, 32, 0, 32, 0, 32, 0, 32, 0])

Tests:

TextDecoder
ToStringFromUTF16_1(bytes);
Concat
ToStringFromUTF16_2(bytes);

Run results for: TextDecoder

TextDecoder

Concat