JavaScriptIf

var x;
if(x){
  //this will not run because x is undefined, (kind of like null in Java) 
}
x = null;
if(x){
  //this will not run because x is null, even though it is defined
}
x = true;
if(x){
  //this will run, because x is defined AND true
}
x = false;
if(x){
  //this will NOT run, because although x is defined, its value is still false
}