为什么setTimeout无法识别函数名称？

Question

(function( $ ){

   $.fn.hash = function(){

   function activate()
   {
      setTimeout('checkHash()', 100);
   }

   activate();

   var previousHashTag = location.hash;

   var previousHashProperty = '';

   function checkHash()
   {
     if( previousHashTag !== location.hash )
     {
        $('body').trigger("hashchange", [ getHashObj() ]);
        previousHashTag = location.hash;
        setTimeout( "checkHash()", 200);
     }
     setTimeout( "checkHash()", 100);
   }

This is my hash plugin I'm trying to make. I would like to call the activate() function when user loads the plugin. The activate function would set a timeout to check for a hash every 100 miliseconds. How can I pull this off since checkHash is outside of the function in this object?

Answer 1

You are passing strings to setTimeout and evaluating them. This breaks the normal scope. Don't do that, pass functions instead.

setTimeout(checkHash, 100);

Now scope will be preserved, and you can access activate from checkHash and vice versa as they are declared in the same scope.

Answer 2

You are using string argument in setTimeout , which means that the code will be run in global object. As your called function is defined inside a closure of another function, you have to pass a reference

setTimeout(checkHash, 100);

or use anonymous function

setTimeout(function(){
  checkHash();
});

You have to use the second approach when you want to pass any arguments to function called from setTimeout .

setTimeout(function(){
  checkHash(arg);
});