How to combine two reals into one in javascript

Combine.js

// some number that when 360 * precision * 100 + 50 * precision won't overflow an integer
// number of positions after the decimal to keep
var digits = 4;
var precision = Math.pow(10, digits);

function combine(x, y, maxydigits) {
	x = Math.floor(x * precision);
	y = Math.floor(y * precision);
	var maxy = Math.pow(10, maxydigits) * precision;
	return x * maxy + y;
}

function extract(z, maxydigits) {
	var maxy = Math.pow(10, maxydigits) * precision;
	var x = Math.floor(z / maxy);
	return {
		x: x / precision,
		y: z % maxy / precision
	}
}


// test
for (var i = 0; i <= 360; i += 0.5) {
	for (var j = 0; j <= 50; j += 0.5) {
		var z = combine(i, j, 3);
		var e = extract(z, 3)
		if (Math.floor(i * precision) !== Math.floor(e.x * precision) || Math.floor(j * precision) !== Math.floor(e.y * precision)) {
			console.log('Failed on ' + i + ', ' + j + ': ' + z, ' # ' + e.x + ', ' + e.y);
			return;
		}
	}
}