How to check element exists?

Question

I need to check if element (#idname) exists, then alert a message to user before closing current tab (or browser).

Here is my condition:

if (document.contains(document.getElementById("#idname"))) {
    window.onbeforeunload = function(evt) {
      // some code here
}

The above code works as well, but my problem is that element (#idname) isn't exist in the HTML in first and I will append it to my HTML after page loading. Now that condition doesn't work anymore. Is there any solution?

You should use getElementById("idname") instead of getElementById("#idname"), shouldn't you? The "#idname" is jQuery syntax. — Nikolay Ermakov
– Nikolay Ermakov, Commented Jan 19, 2016 at 1:10
you should run your js code after your element has inserted, how is it getting there, something is putting it it in,js maybe ? — fuzzybear
– fuzzybear, Commented Jan 19, 2016 at 1:11
Possible duplicate of Is there an "exists" function for jQuery? — Michał Perłakowski
– Michał Perłakowski, Commented Jan 19, 2016 at 1:13

Ram · Accepted Answer · 2016-01-19 01:12:17Z

2

You can simply check the existence of the element in your onbeforeunload handler:

window.onbeforeunload = function(evt) {
   if ( document.getElementById("idname") ) {
      // ...
   }
}

edited Jan 19, 2016 at 1:12

answered Jan 19, 2016 at 1:09

Ram

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5 Comments

Shafizadeh Over a year ago

Can I ask another question? (it isn't related to the above question, it is a small question which doesn't has enough worth to I ask it on SO)

Shafizadeh Over a year ago

Thanks (my Iranian friend) ..! Well I'm trying to create a small markdown editor (something like SO's textarea), Here is a small demo of that. There is just one button (named Bold) which appends two stars ** around selected/highlighted text.

Shafizadeh Over a year ago

Now, what's the problem? That is: bad-handling-spaces-around-highlighted-text ..! To solve that problem, I have created a regex to handle spaces as well like this: $textarea.val( $textarea.val().replace(/\s*(\*+)\s*(.*?)\s*(\*+)\s*/g,' $1$2$3 ') );

Shafizadeh Over a year ago

The above regex should be paste on line 13 of that fiddle and it works as well. But it has a new problme, When I use that regex, the text-highlighting hides after clicking on Bold, Well do you know any workaround to I have both text-highlighting and using that regex?

Ram Over a year ago

The google CDN has been filtered in Iran and the demo isn't run properly for me. Well, let me answer your question tomorrow, It's 5 a.m. and I'm sleepy right now.

Jarlik Stepsto · Accepted Answer · 2016-01-19 01:17:31Z

2

just check if you can select it:

$("#idname").length > 0

or

document.getElementById("idname") === null

You have to do the request inside your function! (See answer of Vohuman)

edited Jan 19, 2016 at 1:17

answered Jan 19, 2016 at 1:08

Jarlik Stepsto

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4 Comments

Ram Over a year ago

It's just an alternative of the OP's current code, it doesn't provide a solution.

Shafizadeh Over a year ago

Yes, @Vohuman is right, .length and === null exactly the same with .contains ..

Jarlik Stepsto Over a year ago

you are right, your answer is what should solve the problem.

Shafizadeh Over a year ago

And please remove # in this line : document.getElementById("# ..

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