In JavaScript, undefined is the default value for variables that have been declared but not initialized. On the other hand, null is an intentional assignment that explicitly indicates the absence of a value. Methods to Check if a Variable is Undefined Using typeof Operator Using Strict Equality...
In this method, we will use the strict equality operator to check whether a variable is null, empty, or undefined. If we dont assign the value to the variable while declaring, the JavaScript compiler assigns it to the undefined value. So, we can check that if the variable contains the ...
As discussed above, users can check if a variable is null or undefined using theOR (||)operator. It checks if the variable satisfies either of the two conditions. When users use it with two Boolean values, the OR operator will return a "true" value if it considers both conditions true. ...
This is why the conditionif (a != null)evaluates totrueifais not equal tonullandundefined. This is the most common use case for the loose equality (==, !==) operators in JavaScript. If you use the loose equality operator to check if two values are not equal, you might get confusing...
If you want to check whether the string is empty/null/undefined, use the following code:let emptyStr; if (!emptyStr) { // String is empty }If the string is empty/null/undefined if condition can return false: Javascript empty string...
We can also check if a variable stores a truthy value. Truthful values are all values that are not false. Falsy values in JavaScript are:undefined,null,false, ,0,""(empty string),NaN(not a number). import{useEffect, useState}from'react'; ...
To check if an array is undefined, you can use the typeof operator to check if the variable holding the array is of type "undefined". To check if an object is undefined, you can use a conditional statement to check if the object is null or undefined....
React Js Check String is Empty | null | undefined - Javascript Example 1 2 const App = () => { 3 const str = " "; 4 let message; 5 if (!str || str.trim() === "") { 6 message = "String is empty"; 7 } else { 8 message = "String has some Value "; 9 } 10 retu...
import * as check from 'guardx/check'; /** * A function that may return undefined */ function findUserById(userId: number): User | undefined { // an operation that may return undefined or the user } const user = findUserById(123); if (check.isNullOrUndefined(user)) { // custom...
Checking if null and undefined Are Primitive or ObjectUsing the custom isPrimitive() function, you can check if null and undefined are a primitive or not in the following way: console.log(isPrimitive(null)); // true console.log(isPrimitive(undefined)); // true ...