This question already has answers here:
Calling a function in JavaScript without parentheses
(7 answers)
Closed 9 years ago.
I have javascript script code here. When I execute my code as it is then it does not trigger func_two function. But when I change following code in func_one
if (this.remove) {
this.func_two;
}
to this
if (this.remove) {
this.func_two();
}
Then it does trigger second function. But I want to trigger it this way this.func_one. IS it possible to do it this way? How?
You have to put () when you call a function, you can't just, out of nowhere, decide that you want it to work another way.
Take a look at this answer, it may help you.
this.func_two;
This statement return the function. It does not call the function. To call the function you have to add () at the end. or you have to do it like:
f2=this.func_two;
f2();
Related
This question already has answers here:
Why does click event handler fire immediately upon page load?
(4 answers)
Closed 3 years ago.
I have two scripts:
<script src="../js/createopp.min.js"></script>
<script src="../js/validation.min.js"></script>
This following line is in the first script, calling a function in the other one:
$('#places').blur(function(){checkPlacesAvailable()});
If I rewrite this as
$('#places').blur(checkPlacesAvailable());
I get a "not defined" error on the function. But I see many examples where the second format is used. Is there something obvious stopping the second version from working in my case?
You should pass function references to event handlers like that.
$('#places').blur(function(){checkPlacesAvailable()});
"is" "equivalent" to this
$('#places').blur(checkPlacesAvailable);
Note that it is not exactly the same because of scopes and all that but most of the times you can pass it in the second manner
This code:
$('#places').blur(checkPlacesAvailable());
start your function immediatly. If you don't want to write "function" you can make this:
$('#places').blur(() => checkPlacesAvailable());
This question already has answers here:
When to use () after a callback function name? [duplicate]
(5 answers)
Closed 6 years ago.
Well I'm starting with jQuery and I'm wondering what is the difference between writing a function with or without parentheses inside a function.
For example if I have the following function:
function test(){
alert("pen pineapple apple pen");
}
This:
$(document).ready(test);
and this:
$(document).ready(test());
both show the same result: "pen pineapple apple pen"
Putting parentheses () at the end of a function causes that function to be invoked immediately, and use its return value in the expression.
This code $(document).ready(test); is using test as a callback function. It essentially says: when the document becomes ready, call the function that I'm providing you with (test).
This code $(document).ready(test()); is immediately invoking the function test, having it return a value, and then passing that value to the ready method. It's possible that test is returning a different function here, which in turn will act as the required callback function. It could also just be an error though, with someone inadvertently including the parentheses when they shouldn't have.
This question already has answers here:
In JavaScript, does it make a difference if I call a function with parentheses?
(5 answers)
Closed 7 years ago.
I'm trying to understand why this code below executes my function as soon as the document is loaded:
var list = document.getElementsByTagName('li');
function yep() {
window.alert('yep');
}
list[0].onclick = yep();
But this does not:
list[0].onclick = yep;
Why does () make a difference when executing a function in this situation?
The parenthesis () execute function immediately. On your second line you are assigning the value of list[0].onclick to the function name but not executing it.
Putting () after a reference to a function means that you want to call the function. Leaving them off means you just want to work with the reference to the function as a value in and of itself.
yep is a reference to a function.
yep() is a directive telling the Javascript engine to execute the yep function.
That's why one executes immediately and the other does not.
This question already has answers here:
What does $(function() {} ); do?
(6 answers)
Closed 9 years ago.
I find the following code in an html document:
<script type="text/javascript">
$(function () {
...
});
I cannot see any intrinsic events like onload = and would like to know how this code is called?
What is the real name and scope of this function and can I call any function defined inside? How?
Whenever you see $ before a function, or $(...).function(...) that usually denotes jQuery.
In the following fiddle I use this code, which is executed on load:
$(function () {
alert("hi!");
});
See here: http://jsfiddle.net/VMZkW/
It is just an anonymous function . In javascript you don't really need to give it a name and because of that after executing once you can never refer it again.
You can have anonymous functions that can be used several times, but not this one. To reuse an anonymous function you just return it to something.
And being an annonymous function it does not create any scope or naming issues and it can access everything according to where it is defined. So you can call outer function too from inside.
This question already has answers here:
setTimeout ignores timeout? (Fires immediately) [duplicate]
(3 answers)
Closed 8 years ago.
I'm working on a Chrome extension to fetch tweets and I figured that I could use the setInterval() function to make the script run every minute. First I tried giving it the function like this:
setInterval(myFunction(), interval);
But it would only execute my script once.
Then out of curiosity I tried declaring the function in the setInterval() function like so:
setInterval(function() {body of my function}, interval);
And that works, but is not a very pretty solution, does anybody any other way of doing this or am I just going to have to deal with it?
Just remove the brackets from the first call. The reason for this is that you need to pass in the function, not the result of the function (what it returns).
When you write the function's name with brackets, it calls the function. When you exclude the brackets, it simply refers to the function like a variable, and so you can pass in your function to the setInterval() function.
setInterval(myFunction, interval);