javascript - Cocos2d JS - Getting vector reflection

I'm working on a small Breakout clone using Cocos2D-JS, without the use of a physics engine.

One of the things that baffles me was how the ball bounces. My friend came up with this:

inputVector - 2(normalVector * inputVector)

I have no idea how to translate that in code. So I tried with this:

g_Ball.position = this.velocityComputer(cc.p(g_Ball.x, g_Ball.y), cc.p(this.x, this.y));

velocityComputer: function(inVector, thisNVector) {
    var prodVec = cc.pDot(inVector, thisNVector);

    var retVec = inVector - (2 * (prodVec * inVector));
    cc.log(retVec);
    // cc.log(blockNVec);
    return retVec;
},

But g_Ball doesn't change directions, and retVec simply logs NaN.

Any suggestions?

Thanks.