function readUtf8String(memory, pointer) { let s = ""; for (i = pointer; memory[i]!==0; i++) { s += String.fromCharCode(memory[i]);

function readUtf8String(memory, pointer) { let s = ""; for (i = pointer; memory[i]!==0; i++) { s += String.fromCharCode(memory[i]); } return s; } This doesn't read UTF-8, this reads bytes and converts them to UTF-16 char codes, so it works only with ASCII or some other 0-255 encoding. To read UTF-8 into a JavaScript string (which is UTF-16), bytes should be properly decoded from UTF-8 (e.g. with TextDecoder).