We can check an html element’s existence through checking its length. If length is greater than 0 that means element exist and if 0 that means does not exist.

Let’s see with an example:

<span id="testId">Let's learn together.</span>

Let’s see the jQuery code :

// Checking for an element which exist.
if( $( "#testId" ).length() > 0 ){
    console.log("testId Exists")
} else { 
    console.log("testId does not Exists").
}

// Checking for another element which does not exist. (Just for better understanding)
if( $( "#testCheckId" ).length() > 0 ){
    console.log("testCheckId Exists")
} else { 
    console.log("testCheckId does not Exists").
}

Output:
testId Exists
testCheckId does not Exists

Here we checked through id but we can also use others like class .