How to check whether an object exists in javascript ?

In this article, we will learn how to check whether an object exists in Javascript. An object contains the key-value pair. The object can be used to check if it exists using 2 approaches: 

• Using the typeof operator
• Using a try-catch statement

Method 1: Using the typeof operator: The typeof operator returns the type of the variable on which it is called as a string. The return string for any object that does not exist is “undefined”. This can be used to check if an object exists or not, as a non-existing object will always return “undefined”. 

Syntax:

if (typeof objectToBeTested != "undefined") 
    // object exists 
else
    // object does not exist 

Example: In this example, we will see the use of typeof operator.

HTML

<h1 style="color: green">
    GeeksforGeeks
</h1>
<b>How to check whether an
    object exists in javascript</b>

<p>Click on the button to
    check if the object exists</p>

<p>Output for existing object:
    <span class="outputExist"></span>
</p>
<p>Output for non existing object:
    <span class="outputNonExist"></span>
</p>

<button onclick="checkObjectExists()">
    Click here
</button>
<script type="text/javascript">
    function checkObjectExists() {
        // create an existing object for comparison
        let existingObject = {};

        if (typeof existingObject != "undefined") {
            ans = true;
        } else {
            ans = false
        }

        document.querySelector(
            '.outputExist').textContent = ans;

        if (typeof nonExistingObject != "undefined") {
            ans = true;
        } else {
            ans = false;
        }

        document.querySelector(
            '.outputNonExist').textContent = ans;
    }
</script>

Output:

How to check whether an object exists in javascript ?

Method 2: Using a try-catch statement to catch a Reference error: Accessing a non-existing object will always throw a Reference error. A try-catch block can be used to determine this error. Any random property of the element can be accessed for this error to be thrown. 

Syntax:

try {
    objectToBeTested.prop;
    // object exists
}
catch {
    // object does not exist
}

Example: In this example, we will see the use of a try-catch statement.

HTML

<h1 style="color: green">
    GeeksforGeeks
</h1>
<b>How to check whether an
    object exists in javascript</b>

<p>Click on the button to check
    if the object exists</p>
<p>Output for existing object:
    <span class="outputExist"></span>
</p>

<p>Output for non existing object:
    <span class="outputNonExist"></span>
</p>

<button onclick="checkObjectExists()">Click here</button>
<script type="text/javascript">
    function checkObjectExists() {

        // create an existing object for comparison
        let existingObject = {};

        try {
            // accessing a random property
            existingObject.prop;
            ans = true;
        } catch {
            ans = false;
        }

        document.querySelector(
            '.outputExist').textContent = ans;

        try {
            // accessing a random property
            nonExistingObject.prop;
            ans = true;
        } catch {
            ans = false;
        }

        document.querySelector(
            '.outputNonExist').textContent = ans;

    }
</script>

Output:

How to check whether an object exists in javascript ?