Difference between setTimeout with and without quotes and parentheses

Using or setIntervalsetTimeout

You should pass a reference to a function as the first argument for or . This reference may be in the form of:setTimeoutsetInterval

• An anonymous function

  setTimeout(function(){/* Look mah! No name! */},2000);
  

• A name of an existing function

  function foo(){...}
  
  setTimeout(foo, 2000);
  

• A variable that points to an existing function

  var foo = function(){...};
  
  setTimeout(foo, 2000);
  

  _{Do note that I set "variable in a function" separately from "function name". It's not apparent that variables and function names occupy the same namespace and can clobber each other.}

Passing arguments

To call a function and pass parameters, you can call the function inside the callback assigned to the timer:

setTimeout(function(){
  foo(arg1, arg2, ...argN);
}, 1000);

There is another method to pass in arguments into the handler, however it's not cross-browser compatible.

setTimeout(foo, 2000, arg1, arg2, ...argN);

Callback context

By default, the context of the callback (the value of inside the function called by the timer) when executed is the global object . Should you want to change it, use .thiswindowbind

setTimeout(function(){
  this === YOUR_CONTEXT; // true
}.bind(YOUR_CONTEXT), 2000);

Security

Although it's possible, you should not pass a string to or . Passing a string makes or use a functionality similar to eval() that executes strings as scripts, making arbitrary and potentially harmful script execution possible. setTimeoutsetIntervalsetTimeout()setInterval()

i think the setTimeout function that you write is not being run. if you use jquery, you can make it run correctly by doing this :

    function alertMsg() {
      //your func
    }

    $(document).ready(function() {
       setTimeout(alertMsg,3000); 
       // the function you called by setTimeout must not be a string.
    });