What is function of var in javascript [closed]

when I write this code answer wilL be 3,

Var gameLevel=1;
Var gameLevel=2;
 Var gameLevel=3;
alert("your game level is: " + gameLevel);

and when I write same problem without Var then again answer same,

Var gameLevel=1;
gameLevel=2;
gameLevel=3;
alert("your game level is: " + gameLevel);

can anyone answered me what has been happening here?