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.
< 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:
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.
< 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: