A simple Uint8Array based bitstream JavaScript class

BitStream.js

// Usage:
// var buf = new Uint8Array(128);
// var bitstream = new BitStream(buf);
// bitstream.writeBits(12, 0xffff);
// bitstream.seekTo(0);
// bitstream.readBits(6); // 111111
// bitstream.readBits(10); // 1111110000

window.BitStream = function(uint8Array) {

	this.a = uint8Array;
	this.position = 0;
	this.bitsPending = 0;

};

window.BitStream.prototype = {

	writeBits: function(bits, value) {
		if (bits == 0) { return; }
		value &= (0xffffffff >>> (32 - bits));
		var bitsConsumed;
		if (this.bitsPending > 0) {
			if (this.bitsPending > bits) {
				this.a[this.position - 1] |= value << (this.bitsPending - bits);
				bitsConsumed = bits;
				this.bitsPending -= bits;
			} else if (this.bitsPending == bits) {
				this.a[this.position - 1] |= value;
				bitsConsumed = bits;
				this.bitsPending = 0;
			} else {
				this.a[this.position - 1] |= value >> (bits - this.bitsPending);
				bitsConsumed = bitsPending;
				this.bitsPending = 0;
			}
		} else {
			bitsConsumed = Math.min(8, bits);
			this.bitsPending = 8 - bitsConsumed;
			this.a[this.position++] = (value >> (bits - bitsConsumed)) << this.bitsPending;
		}
		bits -= bitsConsumed;
		if (bits > 0) {
			this.writeBits(bits, value);
		}
	},

	readBits: function(bits, bitBuffer) {
		if (typeof bitBuffer == "undefined") { bitBuffer = 0; }
		if (bits == 0) { return bitBuffer; }
		var partial;
		var bitsConsumed;
		if (this.bitsPending > 0) {
			var byte = this.a[this.position - 1] & (0xff >> (8 - this.bitsPending));
			bitsConsumed = Math.min(this.bitsPending, bits);
			this.bitsPending -= bitsConsumed;
			partial = byte >> this.bitsPending;
		} else {
			bitsConsumed = Math.min(8, bits);
			this.bitsPending = 8 - bitsConsumed;
			partial = this.a[this.position++] >> this.bitsPending;
		}
		bits -= bitsConsumed;
		bitBuffer = (bitBuffer << bitsConsumed) | partial;
		return (bits > 0) ? this.readBits(bits, bitBuffer) : bitBuffer;
	},

	seekTo: function(bitPos) {
		this.position = (bitPos / 8) | 0;
		this.bitsPending = bitPos % 8;
		if(this.bitsPending > 0) {
			this.bitsPending = 8 - this.bitsPending;
			this.position++;
		}
	}

};