If you do not know that you are creating a global variable (which in most cases is considered bad practice, anyway), this is not normal.
If you came from a language like Java, it’s natural to do something like:
int foo = bar = 0;
Both foo and bar will be initialized to 0, as inside the current scope. But in Javascript:
var foo = bar = 0;
Creates the foo variable inside the current scope and the bar global variable.
Problem
I debugged the game that I write for about an hour before I realized my mistake. I had code like:
function Player() { var posX = posY = 0; } function Bullet() { var posX = posY = 0; } var player = new Player; var bullet = new Bullet;
The variable posY is global. Any method on one object that changes the value of posY will also change it for another object.
What happened: every time a bullet object moved vertically across the screen (changing what it should have been its own posY), the player’s object was teleported to the Y bullet coordinate.
Solved by simply dividing the variable declaration by:
var posX = 0; var posY = 0;