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...
One of the simplest ways to check if a variable is undefined is by using thetypeofoperator. This operator returns a string that indicates the type of the unevaluated operand. If the variable is not defined,typeofwill return the string “undefined”. ...
In the above example, we have used the first if statement to check if the "a" variable is either undefined or null. If it satisfies either of the conditions, then the if block will execute; otherwise, the else block will execute. In the second statement, we have used the if statement ...
In JavaScript, there are 6 data types that are primitives. string number bigint boolean undefined symbol #Non-Primitives (Objects) MDN: Object refers to a data structure containing data and instructions for working with the data. They are stored by reference ...
Most of the developers use the typeof method to check if the type of the property is undefined or not. If the object has the property with the undefined value, typeof is not recommended.Javascript typeof method with undefined1 2 3 4 5 6 7 8 9 10 let myObj = { welcome...
Learn different ways to know if an object has a property and know which of the provided methods is faster. Till the date, there are 3 ways to check if an object has a property : Compare withtypeofandundefined. UsehasOwnPropertymethod. ...
Topic: JavaScript / jQueryPrev|NextAnswer: Use the typeof operatorIf you want to check whether a variable has been initialized or defined (i.e. test whether a variable has been declared and assigned a value) you can use the typeof operator....
If you don't want it to throw a TypeError, you can add an extra check:let value; value // 👈 null and undefined check && Object.keys(value).length === 0 && value.constructor === Object; value = null; // null value = undefined; // undefined ...
functionisFruit(fruitName){letfruits=['Apple','Mango','Pear','Peach'];if(fruits.indexOf(fruitName)>-1){returntrue;}else{returnfalse;}}isFruit('Pear');isFruit('Cat'); Output: truefalse Using the.includes()Function to Check if Array Contains Value in JavaScript ...
//code to check if a value exists in an array using includes function array.includes('hello'); // true array.includes(300); // true array.includes(0); // true array.includes(undefined); // true array.includes(null); // true array.includes(symbol); // true Using indexOf() array...