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"> zambiatek</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"> zambiatek</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 ?
