全局变量在匿名函数中不起作用

Question

var count = 0; 
for ( var i = 0; i < 4; i++ ) { 
  setTimeout(function(){ 
    assert( i == count++, "Check the value of i." ); 
  }, i * 200); 
}

Why doesnt this work( i comes equal to 4 rather than equal to count every time)? count, var are created in a global scope so why would they not be available inside the function?

(I would like an explanation as to why this doesn't work, I found a way to get it to work by wrapping it in another function, just wanting to understand)

Answer 1

Use this; Value of i will be 4 inside each setTime out as for loop already finished and value of

Anonymous function will preserve variable inside it by creating new context.

var count = 0; 
for ( var i = 0; i < 4; i++ ) { 
  (function(i){
     setTimeout(function(){ 
            assert( i == count++, "Check the value of i." ); 
      }, i * 200);
  })(i); 
}