What does !== undefined mean in JavaScript ? Last Updated : 12 Feb, 2024 Comments Improve Suggest changes Like Article Like Report In JavaScript, !== is a strict inequality operator, and undefined is a special value representing the absence of a value or the lack of an assigned value to a variable. The !== operator checks for both value and type equality, and !== undefined is used to verify if a variable is not equal to the undefined value. Table of Content Using Strict InequalityUsing Equality Operator with NegationUsing strict inequalityThe !== operator checks for both value and type equality, and !== undefined is used to verify if a variable is not equal to the undefined value. Example: To demonstrate the use of the strict inequality operator by checking whether a number is undefined or not. JavaScript let num = 5; if (num !== undefined) { console.log(num); } else { console.log(undefined); } Output5 Using equality operator with negationThe non-strict equality operator != lead to unexpected behaviour in certain cases. Using the strict inequality operator !== is generally recommended for checking against undefined. Example: To demonstrate using equality operator with negation. JavaScript let num; if (num != undefined) { console.log("num has a value assigned."); } else { console.log("num is undefined."); } Outputnum is undefined. Comment More infoAdvertise with us Next Article What does !== undefined mean in JavaScript ? A anjugaeu01 Follow Improve Article Tags : JavaScript Web Technologies javascript-operators Similar Reads What is Undefined X 1 in JavaScript ? JavaScript is one of the most popular lightweight, interpreted compiled programming languages. It is single-threaded and synchronous in nature. Scripts(program in JavaScript) re executed as plain text. They can be either written directly on our page or in an external JavaScript file. JavaScript can 2 min read Undefined in JavaScript Undefined is a type of Data type in JavaScript. It is a primitive value undefined, when a variable is declared and not initialized or not assigned with any value. By default, the variable was stored with an Undefined value. Undefined is a global read-only variable that represents the value Undefined 2 min read Undefined Vs Null in JavaScript In JavaScript, both undefined and null represent the absence of a meaningful value, but they have different purposes and are used in distinct contexts. Knowing when and how to use each can help you write clearer, more predictable code. Let's see the differences between undefined and null in JavaScri 4 min read What are undeclared and undefined variables in JavaScript? Undefined: It occurs when a variable has been declared but has not been assigned any value. Undefined is not a keyword. Undeclared: It occurs when we try to access any variable that is not initialized or declared earlier using the var or const keyword. If we use 'typeof' operator to get the value of 1 min read What is (~~) "double tilde" operator in JavaScript ? This is a special kind of operator in JavaScript. To understand the double tilde operator, first, we need to discuss the tilde operator or Bitwise NOT. The (~) tilde operator takes any number and inverts the binary digits, for example, if the number is (100111) after inversion it would be (011000). 3 min read How to check for "undefined" value in JavaScript ? In JavaScript, undefined is a primitive value that represents the absence of a value or the uninitialized state of a variable. It's typically used to denote the absence of a meaningful value, such as when a variable has been declared but not assigned a value. It can also indicate the absence of a re 2 min read JavaScript undefined Property The undefined property is used to check if a value is assigned to a variable or not. Syntax: var x; if (typeof x === "undefined") { txt = "x is undefined"; } else { txt = "x is defined"; } Return Value: It returns 'defined' if the variable is assigned any value and 'undefined' if the variable is not 1 min read What does OR Operator || in a Statement in JavaScript ? JavaScript is a dynamic programming language that allows developers to write complex code with ease. One of the fundamental concepts in JavaScript is the use of operators, which are symbols that perform operations on one or more values. One such operator is the || (logical OR) operator, which can be 6 min read What are the Gotchas in JavaScript ? Javascript truly is a popular language due to its simplicity and versatility. Despite having many merits, Javascript is a funny language that can confuse you at times especially for those accustomed to the traditional OOP language. The tricky parts or 'gotchas' (not limited to the following) are: == 3 min read Like