How can I pass a parameter to a setTimeout() callback?

Question

I have some JavaScript code that looks like:

function statechangedPostQuestion()
{
  //alert("statechangedPostQuestion");
  if (xmlhttp.readyState==         


        

Answer 1

Some answers are correct but convoluted.

I am answering this again, 4 years later, because I still run into overly complex code to solve exactly this question. There IS an elegant solution.

First of all, do not pass in a string as the first parameter when calling setTimeout because it effectively invokes a call to the slow "eval" function.

So how do we pass in a parameter to a timeout function? By using closure:

settopic=function(topicid){
  setTimeout(function(){
    //thanks to closure, topicid is visible here
    postinsql(topicid);
  },4000);
}

...
if (xhr.readyState==4){
  settopic(xhr.responseText);
}

Some have suggested using anonymous function when calling the timeout function:

if (xhr.readyState==4){
  setTimeout(function(){
    settopic(xhr.responseText);
  },4000);
}

The syntax works out. But by the time settopic is called, i.e. 4 seconds later, the XHR object may not be the same. Therefore it's important to pre-bind the variables.