Why does my IF not recognise my condition?

Hello there,

For some reason, the condition in my if statement causes my btn_MC to align to co-ords 0,0

It sits at 240,240 before the movie is previewed, then appears at 0,0 when the movie starts.

if ([button._x = 0 , button._y = 0])
{
button.onRelease = function ()
{

Why oh Why, because if x does = 0 then I want my MC to move elsewhere onRelease…

Could someone please help my daftness!