function smootherstep( x, min, max ) {

	if ( x <= min ) return 0;
	if ( x >= max ) return 1;

	x = ( x - min ) / ( max - min );

	return x * x * x * ( x * ( x * 6 - 15 ) + 10 );

}
A [variation on smoothstep]{@link https://en.wikipedia.org/wiki/Smoothstep#Variations}
that has zero 1st and 2nd order derivatives at x=0 and x=1.

@param {number} x - The value to evaluate based on its position between min and max.
@param {number} min - The min value. Any x value below min will be `0`.
@param {number} max - The max value. Any x value above max will be `1`.
@return {number} The alternated value.