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, Jan 19 '16 at 01:10
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, Jan 19 '16 at 01:11
Possible duplicate of [Is there an "exists" function for jQuery?](http://stackoverflow.com/questions/31044/is-there-an-exists-function-for-jquery) — Michał Perłakowski, Jan 19 '16 at 01:13
@Gothdo My question isn't only about existing, that's about existing of an element which will be created after page-loading. So, don't seem duplicate. — Shafizadeh, Jan 19 '16 at 01:23

Jarlik Stepsto · Answer 1 · 2016-01-19T01:17:31.780

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 '16 at 01:17

answered Jan 19 '16 at 01:08

Jarlik Stepsto

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It's just an alternative of the OP's current code, it doesn't provide a solution. – Ram Jan 19 '16 at 01:11
Yes, @Vohuman is right, `.length` and `=== null` exactly the same with `.contains` .. – Shafizadeh Jan 19 '16 at 01:13
you are right, your answer is what should solve the problem. – Jarlik Stepsto Jan 19 '16 at 01:13
And please remove `#` in this line : `document.getElementById("# ..` – Shafizadeh Jan 19 '16 at 01:17

Ram · Accepted Answer · 2016-01-19T01:12:17.680

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 '16 at 01:12

answered Jan 19 '16 at 01:09

Ram

143,282
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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 Jan 19 '16 at 01:25
Thanks *(my Iranian friend)* ..! Well I'm trying to create a small markdown editor *(something like SO's textarea)*, [Here is a small demo](http://jsfiddle.net/3g3gf7kq/8/) of that. There is just one button *(named Bold)* which appends two stars `**` around selected/highlighted text. – Shafizadeh Jan 19 '16 at 01:35
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 Jan 19 '16 at 01:35
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? – Shafizadeh Jan 19 '16 at 01:36
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. – Ram Jan 19 '16 at 01:47

How to check element exists?

2 Answers2