How to check for an ID in a document via JQuery?

var existeFundoIndex = document.getElementById('fundo_index');

This is the way to tell if there is an element on the page with the ID fundo_index . It's pure, native JavaScript. For simple things like this you do not need jQuery.

If the element exists then the variable will have a pointer to that element, ie it will have boolean value true , if it does not exist it will have the value null .

You can make logic around it, or test other elements. For example:

var existeFundoIndex = document.getElementById('fundo_index');
if (existeFundoIndex){
   // fazer algo
} else {
   // fazer outra coisa
}

Or:

var existeFundoIndex = document.getElementById('fundo_index');
var existeFundoBase = document.getElementById('fundo_base');
if (existeFundoIndex){
   // fazer algo
} else if (existeFundoBase) {
   // fazer outra coisa
} else {
  alert('Não há nenhum!...);
}

Or another variant you need ...

More info:

• document.getElementById() in MDN In English

Use $(seletor).length to check the amount of elements that according to selector switch. A id is unique per document, so the value obtained when calling length can only be: 1 in case the element is present in html or 0 if it does not exist.

$(function(){
  if($('#fundo_index').length)
    console.log('tem #fundo_index');
});

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

<div id='fundo_index'>
  <!-- ... -->
</div>

You do not necessarily need to use jQuery for this.

if(document.getElementById('fundo_index'))
    //elemento com id "fundo_index" existe
else
    //elemento com id "fundo_index" não existe

You can use has-attribute . After all, the ID is an attribute anyway.

This link has the example: Has Attribute