How can I pass a parameter to a setTimeout() callback?
I have some JavaScript code that looks like:
function statechangedPostQuestion()
{
//alert("statechangedPostQuestion");
if (xmlhttp.readyState==4)
{
var topicId = xmlhttp.responseText;
setTimeout("postinsql(topicId)",4000);
}
}
function postinsql(topicId)
{
//alert(topicId);
}
I get a error that topicId is not defined Everything was working before i used the setTimeout() function.
I want my postinsql(topicId) function to be called after some time. What should i do?
setTimeout(function() {
postinsql(topicId);
}, 4000)
You need to feed an anonymous function as a parameter instead of a string, the latter method shouldn't even work per the ECMAScript specification but browsers are just lenient. This is the proper solution, don't ever rely on passing a string as a 'function' when using setTimeout() or setInterval() , it's slower because it has to be evaluated and it just isn't right.
UPDATE:
As Hobblin said in his comments to the question, now you can pass arguments to the function inside setTimeout using Function.prototype.bind()
Example:
setTimeout(postinsql.bind(null, topicId), 4000);
In modern browsers, the "setTimeout" receives a third parameter that is sent as parameter to the internal function at the end of the timer.
Example:
var hello = "Hello World";
setTimeout(alert, 1000, hello);After doing some research and testing, the only correct implementation is:
setTimeout(yourFunctionReference, 4000, param1, param2, paramN);
setTimeout will pass all extra parameters to your function so they can be processed there.
The anonymous function can work for very basic stuff, but within instance of a object where you have to use "this", there is no way to make it work. Any anonymous function will change "this" to point to window, so you will lose your object reference.
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