How to use strings with JavaScript Typed Arrays

Question

I've come across a problem in that I don't see a way to easily convert strings to typed arrays, and converting from typed arrays to strings appears to be a real pain requiring a manual char code conversion for every byte. Is there any better methods to convert strings to typed arrays or vise-versa?

Example:

I have a UTF8 encoded string, "Something or other", and I want to write it to an ArrayBuffer in length then string format.

Answer 1

This should solve your problem

How to use strings with JavaScript Typed Arrays

JS Strings are stored in UTF-16 encoding where each character takes 2 bytes. String.charCodeAt returns these 2-byte Unicodes. This is how to read UTF-16 encoded strings from a DataView:

DataView.prototype.getUTF16String = function(offset, length) {
    var utf16 = new ArrayBuffer(length * 2);
    var utf16View = new Uint16Array(utf16);
    for (var i = 0; i < length; ++i) {
        utf16View[i] = this.getUint8(offset + i);
    }
    return String.fromCharCode.apply(null, utf16View);
};

and these functions to convert string to and from arraybuffer

    function ab2str(buf) {
       return String.fromCharCode.apply(null, new Uint16Array(buf));
     }

    function str2ab(str) {
       var buf = new ArrayBuffer(str.length*2); // 2 bytes for each char
       var bufView = new Uint16Array(buf);
       for (var i=0, strLen=str.length; i<strLen; i++) {
         bufView[i] = str.charCodeAt(i);
       }
       return buf;
     }

Answer 2

You can use TextEncoder and TextDecoder, it was originally only implemented in Firefox, but has since gained wider support. This two full years after your initial question :)

Fortunately, there exists a polyfill that does the job.

var initialString = "Something or other";

var utf8EncodedString = new TextEncoder("utf-8").encode(initialString);

// utf8EncodedString is a Uint8Array, so you can inspect
// the individual bytes directly:
for (var i = 0; i < utf8EncodedString.length; ++i) {
    console.log(utf8EncodedString[i]);
}

var decodedString = new TextDecoder("utf-8").decode(utf8EncodedString);

if (initialString !== decodedString) {
    console.error("You're lying!");
}

Answer 3

If you are willing to use external libraries, you can take a look at jDataView which supports reading strings in different encodings from a TypedArray and handles endianness conversion as well.