function modf( x ) {
	return fcn( x, [ 0.0, 0.0 ], 1, 0 );
}
Decomposes a double-precision floating-point number into integral and fractional parts, each having the same type and sign as the input value.

@param {number} x - input value
@returns {Array<number>} output array

@example
var parts = modf( 3.14 );
// returns [ 3.0, 0.14000000000000012 ]