Random color generator

Question

Given this function, I want to replace the color with a random color generator.

document.overlay = GPolyline.fromEncoded({
    color: "#0000FF",
    weight: 10,
    points: encoded_points,
    zoomFactor: 32,
    levels: encoded_levels,
    numLevels: 4
});

How can I do it?

Answer 1

Use getRandomColor() in place of "#0000FF":

function getRandomColor() {
  var letters = '0123456789ABCDEF';
  var color = '#';
  for (var i = 0; i < 6; i++) {
    color += letters[Math.floor(Math.random() * 16)];
  }
  return color;
}



function setRandomColor() {
  $("#colorpad").css("background-color", getRandomColor());
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="colorpad" style="width:300px;height:300px;background-color:#000">

</div>
<button onclick="setRandomColor()">Random Color</button>

Answer 2

I doubt anything will be faster or shorter than this one:

"#" + ((1<<24)*Math.random() | 0).toString(16)

Challenge!

Answer 3

Here is another take on this problem.

My goal was to create vibrant and distinct colors. To ensure the colors are distinct I avoid using a random generator and select "evenly spaced" colors from the rainbow.

This is perfect for creating pop-out markers in Google Maps that have optimal "uniqueness" (that is, no two markers will have similar colors).

function rainbow(numOfSteps, step) {
    // This function generates vibrant, "evenly spaced" colours (i.e. no clustering). This is ideal for creating easily distinguishable vibrant markers in Google Maps and other apps.
    // Adam Cole, 2011-Sept-14
    // HSV to RBG adapted from: http://mjijackson.com/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript
    var r, g, b;
    var h = step / numOfSteps;
    var i = ~~(h * 6);
    var f = h * 6 - i;
    var q = 1 - f;
    switch(i % 6){
        case 0: r = 1; g = f; b = 0; break;
        case 1: r = q; g = 1; b = 0; break;
        case 2: r = 0; g = 1; b = f; break;
        case 3: r = 0; g = q; b = 1; break;
        case 4: r = f; g = 0; b = 1; break;
        case 5: r = 1; g = 0; b = q; break;
    }
    var c = "#" + ("00" + (~ ~(r * 255)).toString(16)).slice(-2) + ("00" + (~ ~(g * 255)).toString(16)).slice(-2) + ("00" + (~ ~(b * 255)).toString(16)).slice(-2);
    return (c);
}

If you wish to see what this looks like in action see Simple JavaScript Rainbow Color Generator for Google Map Markers.

Answer 4

Who can beat it?

'#' + Math.random().toString(16).substr(-6);

It is guaranteed to work all the time: http://jsbin.com/OjELIfo/2/edit

Based on eterps's comment, the code above can still generate shorter strings if the hexadecimal representation of the random color is very short (0.730224609375 => 0.baf).

This code should work in all cases:

function makeRandomColor(){
  var c = '';
  while (c.length < 7) {
    c += (Math.random()).toString(16).substr(-6).substr(-1)
  }
  return '#' + c;
}

Answer 5

You can also use HSL available on every good browser (http://caniuse.com/#feat=css3-colors)

function randomHsl() {
    return 'hsla(' + (Math.random() * 360) + ', 100%, 50%, 1)';
}

This will give you only bright colors, you can play around with the brightness, saturation and alpha.

// es6
const randomHsl = () => `hsla(${Math.random() * 360}, 100%, 50%, 1)`

Answer 6

There is no need for a hash of hexadecimal letters. JavaScript can do this by itself:

function get_random_color() {
  function c() {
    var hex = Math.floor(Math.random()*256).toString(16);
    return ("0"+String(hex)).substr(-2); // pad with zero
  }
  return "#"+c()+c()+c();
}

Answer 7

I like this one: '#' + (Math.random().toString(16) + "000000").substring(2,8)

Answer 8

Random color generation with brightness control:

function getRandColor(brightness){

    // Six levels of brightness from 0 to 5, 0 being the darkest
    var rgb = [Math.random() * 256, Math.random() * 256, Math.random() * 256];
    var mix = [brightness*51, brightness*51, brightness*51]; //51 => 255/5
    var mixedrgb = [rgb[0] + mix[0], rgb[1] + mix[1], rgb[2] + mix[2]].map(function(x){ return Math.round(x/2.0)})
    return "rgb(" + mixedrgb.join(",") + ")";
}

Answer 9

The article written by Paul Irish, Random Hex Color Code Generator in JavaScript, is absolutely amazing. Use:

'#' + Math.floor(Math.random()*16777215).toString(16).padStart(6, '0');

Thanks to Haytam for sharing the padStart to solve the hexadecimal code length issue.

Answer 10

'#'+Math.random().toString(16).slice(-3) // three-numbers format aka #f3c
'#'+Math.random().toString(16).slice(-6) // six-number format aka #abc123

Answer 11

If you're a noob like me, clueless about hexadecimals and such, this might be more intuitive.

function r() { return Math.floor(Math.random() * 255) }

var color = 'rgb(' + r() + "," + r() + "," + r() + ')';

You just need to end up with a string such as 'rgb(255, 123, 220)'

Answer 12

Here's a twist on the solution provided by @Anatoliy.

I needed to generate only light colours (for backgrounds), so I went with three letter (#AAA) format:

function get_random_color() {
    var letters = 'ABCDE'.split('');
    var color = '#';
    for (var i=0; i<3; i++ ) {
        color += letters[Math.floor(Math.random() * letters.length)];
    }
    return color;
}

Answer 13

Use:

function random_color(format)
{
    var rint = Math.round(0xffffff * Math.random());
    switch(format)
    {
        case 'hex':
            return ('#0' + rint.toString(16)).replace(/^#0([0-9a-f]{6})$/i, '#$1');
            break;

        case 'rgb':
            return 'rgb(' + (rint >> 16) + ',' + (rint >> 8 & 255) + ',' + (rint & 255) + ')';
            break;

        default:
            return rint;
            break;
    }
}

Updated version:

function random_color( format ){
  var rint = Math.floor( 0x100000000 * Math.random());
  switch( format ){
    case 'hex':
      return '#' + ('00000'   + rint.toString(16)).slice(-6).toUpperCase();
    case 'hexa':
      return '#' + ('0000000' + rint.toString(16)).slice(-8).toUpperCase();
    case 'rgb':
      return 'rgb('  + (rint & 255) + ',' + (rint >> 8 & 255) + ',' + (rint >> 16 & 255) + ')';
    case 'rgba':
      return 'rgba(' + (rint & 255) + ',' + (rint >> 8 & 255) + ',' + (rint >> 16 & 255) + ',' + (rint >> 24 & 255)/255 + ')';
    default:
      return rint;
  }
}

Answer 14

var color = "#";
for (k = 0; k < 3; k++) {
    color += ("0" + (Math.random()*256|0).toString(16)).substr(-2);
}

A breakdown of how this works:

Math.random()*256 gets a random (floating point) number from 0 to 256 (0 to 255 inclusive)
Example result: 116.15200161933899

Adding the |0 strips off everything after the decimal point.
Ex: 116.15200161933899 -> 116

Using .toString(16) converts this number to hexadecimal (base 16).
Ex: 116 -> 74
Another ex: 228 -> e4

Adding "0" pads it with a zero. This will be important when we get the substring, since our final result must have two characters for each color.
Ex: 74 -> 074
Another ex: 8 -> 08

.substr(-2) gets just the last two characters.
Ex: 074 -> 74
Another ex: 08 -> 08 (if we hadn't added the "0", this would have produced "8" instead of "08")

The for loop runs this loop three times, adding each result to the color string, producing something like this:
#7408e4

Answer 15

A short answer with padding to the exact size:

'#' + ((1<<24)*(Math.random()+1)|0).toString(16).substr(1)

Answer 16

The top voted comment of the top answer suggests that Martin Ankerl's approach is better than random hex numbers, and although I haven't improved on Ankerl's methodology, I have successfully translated it to JavaScript.

I figured I'd post an additional answer to this already mega-sized Stack Overflow question because the top answer has another comment linking to a Gist with the JavaScript implementation of Ankerl's logic and that link is broken (404). If I had the reputation, I would have simply commented the jsbin link I created.

// Adapted from
// http://jsfiddle.net/Mottie/xcqpF/1/light/
const rgb2hex = (rgb) => {
  return (rgb && rgb.length === 3) ? "#" +
    ("0" + parseInt(rgb[0],10).toString(16)).slice(-2) +
    ("0" + parseInt(rgb[1],10).toString(16)).slice(-2) +
    ("0" + parseInt(rgb[2],10).toString(16)).slice(-2) : '';
}

// The next two methods are converted from Ruby to JavaScript.
// It is sourced from http://martin.ankerl.com/2009/12/09/how-to-create-random-colors-programmatically/

// # HSV values in [0..1[
// # returns [r, g, b] values from 0 to 255
const hsv_to_rgb = (h, s, v) => {
  const h_i = Math.floor(h*6)
  const f = h*6 - h_i
  const p = v * (1 - s)
  const q = v * (1 - (f * s))
  const t = v * (1 - (1 - f) * s)
  let r, g, b
  switch(h_i) {
    case(0):
      [r, g, b] = [v, t, p]
      break
    case(1):
      [r, g, b] = [q, v, p]
      break
    case(2):
      [r, g, b] = [p, v, t]
      break
    case(3):
      [r, g, b] = [p, q, v]
      break
    case(4):
      [r, g, b] = [t, p, v]
      break
    case(5):
      [r, g, b] = [v, p, q]
      break
  }
  return [Math.floor(r * 256), Math.floor(g * 256), Math.floor(b * 256)]
}

// # Use the golden ratio
const golden_ratio_conjugate = 0.618033988749895
let h = Math.random() // # Use a random start value
const gen_hex = (numberOfColors) => {
  const colorArray = []
  while (numberOfColors > 0) {
    h += golden_ratio_conjugate
    h %= 1
    colorArray.push(rgb2hex(hsv_to_rgb(h, 0.99, 0.99)))
    numberOfColors -= 1
  }
  console.log(colorArray)
  return colorArray
}

gen_hex(100)

https://jsbin.com/qeyevoj/edit?js,console

Answer 17

map

always returns a valid RGB color:

`rgb(${[1,2,3].map(x=>Math.random()*256|0)})`

let c= `rgb(${[1,2,3].map(x=>Math.random()*256|0)})`

console.log(c);
document.body.style.background=c

Answer 18

regexp

always returns a valid hex 6-digit color

"#xxxxxx".replace(/x/g, y=>(Math.random()*16|0).toString(16))

let c= "#xxxxxx".replace(/x/g, y=>(Math.random()*16|0).toString(16));
       
console.log(c);
document.body.style.background=c

Answer 19

So whilst all the answers here are good I wanted a bit more control over the output. For instance I'd like to prevent any near white shades, whilst ensuring I get bright vibrant colours not washed out shades.

function generateColor(ranges) {
            if (!ranges) {
                ranges = [
                    [150,256],
                    [0, 190],
                    [0, 30]
                ];
            }
            var g = function() {
                //select random range and remove
                var range = ranges.splice(Math.floor(Math.random()*ranges.length), 1)[0];
                //pick a random number from within the range
                return Math.floor(Math.random() * (range[1] - range[0])) + range[0];
            }
            return "rgb(" + g() + "," + g() + "," + g() +")";
        };

So now I can specify 3 arbitrary ranges to pick rgb values from. You can call it with no arguments and get my default set which will usually generate a quite vibrant colour with once obvious dominant shade, or you can supply your own array of ranges.

Answer 20

There are so many ways you can accomplish this. Here's some I did:

Generates six random hex digits (0-F)

function randColor() {
    for (var i=0, col=''; i<6; i++) {
        col += (Math.random()*16|0).toString(16);
    }
    return '#'+col;
}

Extremely short one-liner

'#'+(Math.random().toString(16)+'00000').slice(2,8)

Generates individual HEX components (00-FF)

function randColor2() {
    var r = ('0'+(Math.random()*256|0).toString(16)).slice(-2),
        g = ('0'+(Math.random()*256|0).toString(16)).slice(-2),
        b = ('0'+(Math.random()*256|0).toString(16)).slice(-2);
    return '#' +r+g+b;
}

Over-engineered hex string (XORs 3 outputs together to form color)

function randColor3() {
    var str = Math.random().toString(16) + Math.random().toString(16),
    sg = str.replace(/0./g,'').match(/.{1,6}/g),
    col = parseInt(sg[0], 16) ^ 
          parseInt(sg[1], 16) ^ 
          parseInt(sg[2], 16);
    return '#' + ("000000" + col.toString(16)).slice(-6);
}

Answer 21

You could use this simple function

function getRandomColor(){
 var color =  "#" + (Math.random() * 0xFFFFFF << 0).toString(16);
 return color;
}

Answer 22

For decent randomness.

Random color

`#${crypto.getRandomValues(new Uint32Array(1))[0].toString(16).padStart(8, 0).slice(-6)}`

Random alpha, random color.

`#${crypto.getRandomValues(new Uint32Array(1))[0].toString(16).padStart(8, 0)}`

Answer 23

Yet another random color generator:

var randomColor;
randomColor = Math.random() * 0x1000000; // 0 < randomColor < 0x1000000 (randomColor is a float)
randomColor = Math.floor(randomColor); // 0 < randomColor <= 0xFFFFFF (randomColor is an integer)
randomColor = randomColor.toString(16); // hex representation randomColor
randomColor = ("000000" + randomColor).slice(-6); // leading zeros added
randomColor = "#" + randomColor; // # added

Answer 24

Use distinct-colors.

It generates a palette of visually distinct colors.

distinct-colors is highly configurable:

• Choose how many colors are in the palette
• Restrict the hue to a specific range
• Restrict the chroma (saturation) to a specific range
• Restrict the lightness to a specific range
• Configure general quality of the palette

Answer 25

Array.prototype.reduce makes it very clean.

["r", "g", "b"].reduce(function(res) {
    return res + ("0" + ~~(Math.random()*256).toString(16)).slice(-2)
}, "#")

---

It needs a shim for old browsers.

Answer 26

function get_random_color() {
    return "#" + (Math.round(Math.random() * 0XFFFFFF)).toString(16);
}

http://jsfiddle.net/XmqDz/1/

Answer 27

My version:

function RandomColor() {
  var hex = (Math.round(Math.random()*0xffffff)).toString(16);
  while (hex.length < 6) hex = "0" + hex;
  return hex;
}

Answer 28

A bit enhanced one-liner to make the approach more vivid

'#' + Math.round((0x1000000 + 0xffffff * Math.random())).toString(16).slice(1)

Answer 29

Almost all of the previous short hand methods are generating invalid hex codes (five digits). I came across a similar technique only without that issue here:

"#"+(((1+Math.random())*(1<<24)|0).toString(16)).substr(-6)

Test

Try this in the console:

for(i = 0; i < 200; i++) {
    console.log("#"+(((1+Math.random())*(1<<24)|0).toString(16)).substr(-6));
}

Answer 30

You should use '#'+Math.floor(Math.random()*16777215).toString(16); for a random color code.

Your thinking, but why 16777215? Check this article: Generate a random color with a single line of JavaScript code

function generateRandomColor()
{
    var randomColor = '#'+Math.floor(Math.random()*16777215).toString(16);
    if(randomColor.length != 7){ // In any case, the color code is invalid
        randomColor = generateRandomColor();
    }
    return randomColor;
    // The random color will be freshly served
}
document.body.style.backgroundColor = generateRandomColor() // -> #E1AC94