phaser/src/math/Percent.js

/**
 * Work out what percentage `value` is of the range between `min` and `max`.
 * If `max` isn't given then it will return the percentage of `value` to `min`.
 *
 * You can optionally specify an `upperMax` value, which is a mid-way point in the range that represents 100%, after which the % starts to go down to zero again.
 *
 * @function Phaser.Math.Percent
 * @since 3.0.0
 *
 * @param {number} value - [description]
 * @param {number} min - [description]
 * @param {number} [max] - [description]
 * @param {number} [upperMax] - [description]
 *
 * @return {float} A value between 0 and 1 representing the percentage.
 */
var Percent = function (value, min, max, upperMax)
{
    if (max === undefined) { max = min + 1; }

    var percentage = (value - min) / (max - min);

    if (percentage > 1)
    {
        if (upperMax !== undefined)
        {
            percentage = ((upperMax - value)) / (upperMax - max);

            if (percentage < 0)
            {
                percentage = 0;
            }
        }
        else
        {
            percentage = 1;
        }
    }
    else if (percentage < 0)
    {
        percentage = 0;
    }

    return percentage;
};

module.exports = Percent;