misc/wasm: add polyfill for TextEncoder/TextDecoder for Edge support

Fixes golang#27295

Author: silbinarywolf

misc/wasm/wasm_exec.js

@@ -27,6 +27,82 @@
 		global.TextEncoder = util.TextEncoder;
 		global.TextDecoder = util.TextDecoder;
 	} else {
+		// Add polyfill for TextEncoder and TextDecoder for Microsoft Edge 17/18 support
+		// https://caniuse.com/#feat=textencoder
+		if (!window.TextEncoder) {
+			TextEncoder = function(){}
+			TextEncoder.prototype.encode = function (string) {
+				var octets = [];
+				var length = string.length;
+				var i = 0;
+				while (i < length) {
+					var codePoint = string.codePointAt(i);
+					var c = 0;
+					var bits = 0;
+					if (codePoint <= 0x0000007F) {
+						c = 0;
+						bits = 0x00;
+					} else if (codePoint <= 0x000007FF) {
+						c = 6;
+						bits = 0xC0;
+					} else if (codePoint <= 0x0000FFFF) {
+						c = 12;
+						bits = 0xE0;
+					} else if (codePoint <= 0x001FFFFF) {
+						c = 18;
+						bits = 0xF0;
+					}
+					octets.push(bits | (codePoint >> c));
+					c -= 6;
+					while (c >= 0) {
+						octets.push(0x80 | ((codePoint >> c) & 0x3F));
+						c -= 6;
+					}
+					i += codePoint >= 0x10000 ? 2 : 1;
+				}
+				return octets;
+			};
+		}
+		if (!window.TextDecoder) {
+			TextDecoder = function(){}
+			TextDecoder.prototype.decode = function (octets) {
+				var string = "";
+				var i = 0;
+				while (i < octets.length) {
+					var octet = octets[i];
+					var bytesNeeded = 0;
+					var 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 (octets.length - i - bytesNeeded > 0) {
+						var k = 0;
+						while (k < bytesNeeded) {
+							octet = octets[i + k + 1];
+							codePoint = (codePoint << 6) | (octet & 0x3F);
+							k += 1;
+						}
+					} else {
+						codePoint = 0xFFFD;
+						bytesNeeded = octets.length - i;
+					}
+					string += String.fromCodePoint(codePoint);
+					i += bytesNeeded + 1;
+				}
+				return string
+			};
+		}
+
 		if (typeof window !== "undefined") {
 			window.global = window;
 		} else if (typeof self !== "undefined") {