GetRandom = function (array, startIndex, length)
{
    if (startIndex === undefined) { startIndex = 0; }
    if (length === undefined) { length = array.length; }

    var randomIndex = startIndex + Math.floor(Math.random() * length);

    return (array[randomIndex] === undefined) ? null : array[randomIndex];
}
Returns a Random element from the array.

@function Phaser.Utils.Array.GetRandom
@since 3.0.0

@generic T
@genericUse {T[]} - [array]
@genericUse {T} - [$return]

@param {T[]} array - The array to select the random entry from.
@param {number} [startIndex=0] - An optional start index.
@param {number} [length=array.length] - An optional length, the total number of elements (from the startIndex) to choose from.

@return {T} A random element from the array, or `null` if no element could be found in the range given.