index.js
function(r, g, b, a) {
    var rgb = [r, g, b].map(function (c) { return number(c); });
    a = number(a);
    if (rgb.some(isNaN) || isNaN(a)) return null;
    rgb.push(a);
    return rgb;
  }
function(r, g, b, a) {
    var rgb = [r, g, b].map(function (c) { return number(c); });
    a = number(a);
    if (rgb.some(isNaN) || isNaN(a)) return null;
    rgb.push(a);
    return rgb;
  }
function ( r , g , b , a ) { var rgb = [ r , g , b ] . map ( function ( c ) { return number ( c ) ; } ) ; a = number ( a ) ; if ( rgb . some ( isNaN ) || isNaN ( a ) ) return null ; rgb . push ( a ) ; return rgb ; }
Given an rgba color as number-like objects, return that array
with numbers if possible, and null otherwise

@param {number} r red
@param {number} g green
@param {number} b blue
@param {number} a alpha
@returns {Array} rgba array
Given an rgba color as number - like objects return that array with numbers if possible and null otherwise