Calculate color HEX having 2 colors and percent/position

Is it possible to calculate a color in a middle of a gradient?

var color1 = 'FF0000';
var color2 = '00FF00';

// 50% between the two colors, should return '808000'
var middle = gradient(color1, color2, 0.5); 

I only have two hex strings, and I want one in return.

Answer

This should work:

It basically involves converting them to decimal, finding the halves, converting the results back to hex and then concatenating them.

var color1 = 'FF0000';
var color2 = '00FF00';
var ratio = 0.5;
var hex = function(x) {
    x = x.toString(16);
    return (x.length == 1) ? '0' + x : x;
};

var r = Math.ceil(parseInt(color1.substring(0,2), 16) * ratio + parseInt(color2.substring(0,2), 16) * (1-ratio));
var g = Math.ceil(parseInt(color1.substring(2,4), 16) * ratio + parseInt(color2.substring(2,4), 16) * (1-ratio));
var b = Math.ceil(parseInt(color1.substring(4,6), 16) * ratio + parseInt(color2.substring(4,6), 16) * (1-ratio));

var middle = hex(r) + hex(g) + hex(b);