Trigger jquery event function without anonymous function

Question

I haven't found an answer to the problem I am trying to understand. I would be thankful if someone can help me: I am working on a JavaScript project and I need to pass an event function as a parameter for a callback function. Is there a way to get this?

I know that this works fine:

function callback(){
    alert("called!");
}
function trigger_callback(message, callback){
    alert(message);
    callback();
}
trigger_callback("I will call a function", callback);

But what I need is something like this:

trigger_callback("I will focus an input", $("#input").focus);

I get the error:

TypeError: this._focus is undefined

So far, I've been using:

trigger_callback("I will focus an input", function(){$("#input").focus();});

I need a simpler way to do it. Also, can someone please explain why this fails?

Taplar · Accepted Answer · 2018-07-20 17:32:58Z

1

var $tester = $('#tester');
var $tester2 = $('#tester2');

//focus is called while attached to the $tester, so it's context (this) is the $tester
$tester.focus();

//grabbing the method, you lose the context
//focusMethod does not have a context of the $tester
//it's context, in this case, would be the window as it's a global variable
var focusMethod = $tester.focus;

try {
  focusMethod();
} catch (e) {
  console.log('expected error');
}

//we can use bind, which will create another instance of the method, but
//will force the context on it to be $tester
var forceContext = $tester2.focus.bind($tester2);

forceContext();

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<input type="text" id="tester">
<input type="text" id="tester2">

answered Jul 20, 2018 at 17:32

Taplar

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1 Comment

WakeupMorning Over a year ago

You are right! I was so close trying to use .bind(this) and .bind($) but I forgot that I must use the element as itself.

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