Compare sort speeds using inline and pre-computed distance calculations.

color-sort.js

// Return a color object
function color(r, g, b) {
  return { 
    r: r,
    g: g,
    b: b
  };
}

// Return a random number between a and b inclusive
function random(a, b) {
  return Math.floor(a + Math.random() * (b + 1 - a));
}

// Return a random hex value
function randomHex() {
  return random(0, 255);
}

// Generate a color using random values
function randomColor() {
  return color(randomHex(), randomHex(), randomHex());
}

// Create an array of random colors of length n
function randomColors(n) {
  var colors = new Array(n);
  while (n--) {
    colors[n] = randomColor();
  }
  return colors;
}

// Pretty stringify
function $$(obj) {
  return JSON.stringify(obj, 0, 4);
}

// Calculate distance between two colors
function getDistance(a, b) {
  var r = b.r - a.r;
  var g = b.g - a.g;
  var b = b.b - a.b;
  return r * r + g * g + b * b;
}

// Sort color distance, calculating distance in the loop
function sortByColorSlow(c, colors) {
  return colors.sort(function(a, b) {
    var aD = getDistance(a, c);
    var bD = getDistance(b, c);
    return aD - bD;
  });
}

// Sort color distance, precomputing distance outside of the loop
function sortByColorFast(c, colors) {

  var i;
  var n = colors.length;

  for (i = 0; i < n; ++i) {
    colors[i]._d = getDistance(c, colors[i]);
  }

  colors.sort(function(a, b) {
    return a._d - b._d;
  });

  // Deleting slows this way down
  // If you don't like adding this property,
  // sort a lookup table instead.
  // for (i = 0; i < n; ++i) {
  //   delete colors[i]._d;
  // }

  return colors;
}

// Count iterations in given time
function _test(fn) {

  var then = Date.now();
  var i = 0;

  do {
    fn();
    i++
  } while ((Date.now() - then) < 1000);

  return i;
}

// Average performance of multiple tests
function test(fn) {
  var i = 0;
  var n = 3;
  var speed = 0;
  for (; i < n; ++i) {
    speed = speed + _test(fn);
  }
  return (speed / n).toFixed(1);
}

// TESTING TIME

// Build catalog
var colors = randomColors(100);

// Create random query
var search = randomColor();

// Test slow sort
var slow = test(function() {
  sortByColorSlow(search, colors.slice());
}, duration);

// Test fast sort
var fast = test(function() {
  sortByColorFast(search, colors.slice());
}, duration);

console.log('slow', slow);
console.log('fast', fast);