Generate gradient color from 2 or 3 colors using JavaScript. Example: https://jsfiddle.net/e18g5f3L/

color-gradient.js

/**
 * You may use this function with both 2 or 3 interval colors for your gradient.
 * For example, you want to have a gradient between Bootstrap's danger-warning-success colors.
 */
function colorGradient(fadeFraction, rgbColor1, rgbColor2, rgbColor3) {
    var color1 = rgbColor1;
    var color2 = rgbColor2;
    var fade = fadeFraction;

    // Do we have 3 colors for the gradient? Need to adjust the params.
    if (rgbColor3) {
      fade = fade * 2;

      // Find which interval to use and adjust the fade percentage
      if (fade >= 1) {
        fade -= 1;
        color1 = rgbColor2;
        color2 = rgbColor3;
      }
    }

    var diffRed = color2.red - color1.red;
    var diffGreen = color2.green - color1.green;
    var diffBlue = color2.blue - color1.blue;

    var gradient = {
      red: parseInt(Math.floor(color1.red + (diffRed * fade)), 10),
      green: parseInt(Math.floor(color1.green + (diffGreen * fade)), 10),
      blue: parseInt(Math.floor(color1.blue + (diffBlue * fade)), 10),
    };

    return 'rgb(' + gradient.red + ',' + gradient.green + ',' + gradient.blue + ')';
  }

Thanks for this. Quickly converted it to TypeScript if anyone is interested:

interface RGBColor {
  red: number;
  green: number;
  blue: number;
}

export const colorGradient = (
  fadeFraction: number,
  rgbColor1: RGBColor,
  rgbColor2: RGBColor,
  rgbColor3?: RGBColor
) => {
  let color1 = rgbColor1;
  let color2 = rgbColor2;
  let fade = fadeFraction;

  // Do we have 3 colors for the gradient? Need to adjust the params.
  if (rgbColor3) {
    fade = fade * 2;

    // Find which interval to use and adjust the fade percentage
    if (fade >= 1) {
      fade -= 1;
      color1 = rgbColor2;
      color2 = rgbColor3;
    }
  }

  let diffRed = color2.red - color1.red;
  let diffGreen = color2.green - color1.green;
  let diffBlue = color2.blue - color1.blue;

  let gradient = {
    red: Math.floor(color1.red + diffRed * fade),
    green: Math.floor(color1.green + diffGreen * fade),
    blue: Math.floor(color1.blue + diffBlue * fade),
  };

  return (
    "rgb(" + gradient.red + "," + gradient.green + "," + gradient.blue + ")"
  );
};