generate a v4 GUID in JS

guidv4.js

// Based on http://stackoverflow.com/questions/105034/create-guid-uuid-in-javascript
var guidv4=(function(_w, lut, i){
	lut = []; for (i=0; i<256; i++) { lut[i] = (i<16?'0':'')+(i).toString(16); }
	var r = Math.random, ui32=0x100000000, _crypto = _w.crypto || _w.msCrypto;
	return function(d) {
		if( _crypto && _crypto.getRandomValues ) {
			try {
				d = new Uint32Array(4);
				_crypto.getRandomValues(d);
			} catch(e) {
				d = 0;
			}
		}
		if( !d ) {
			d = [r()*ui32>>>0, r()*ui32>>>0, r()*ui32>>>0, r()*ui32>>>0];
		}
		return lut[d[0]&0xff]+lut[d[0]>>8&0xff]+lut[d[0]>>16&0xff]+lut[d[0]>>24&0xff]+'-'+
		lut[d[1]&0xff]+lut[d[1]>>8&0xff]+'-'+lut[d[1]>>16&0x0f|0x40]+lut[d[1]>>24&0xff]+'-'+
		lut[d[2]&0x3f|0x80]+lut[d[2]>>8&0xff]+'-'+lut[d[2]>>16&0xff]+lut[d[2]>>24&0xff]+
		lut[d[3]&0xff]+lut[d[3]>>8&0xff]+lut[d[3]>>16&0xff]+lut[d[3]>>24&0xff];
	};
})(window);