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Type of undefined in JavaScript

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In JavaScript, “undefined” is a primitive type that represents a variable that has been declared but not assigned a value. It is also used as the default return value for functions that do not have a return statement or for variables that do not exist.

For example, if you declare a variable but do not assign a value to it, like this:

let myVariable;

Then, if you try to access the value of “myVariable” before assigning a value to it, you will get “undefined”:

console.log(myVariable); // Output: undefined

It’s important to note that “undefined” is a primitive value in JavaScript and not an object. However, it is considered a type of its own in the language.

Type of undefined in JavaScript example

Simple example code that demonstrates the “undefined” type in JavaScript:

<!DOCTYPE html>
    let myVariable; 

    function myFunction() {
        // do not return a value

    let myObject = {}; 



Type of undefined in JavaScript

How to handle undefined in JavaScript?

Answer: In JavaScript, handling “undefined” can be important to prevent unexpected errors or behavior in your code. Here are some common ways to handle “undefined”:

1. Check if a variable is undefined using the “typeof” operator:

let myVariable;
if (typeof myVariable === 'undefined') {
  // handle the undefined variable

2. Use default values when dealing with potentially undefined variables:

let myVariable;
let myValue = myVariable || 'default';

3. Use optional chaining (available from ES2020) to access properties of potentially undefined objects:

let myObject = {
  prop1: {
    prop2: 'value'
let myValue = myObject.prop1?.prop2; // use "?" to handle undefined object properties

4. Return a default value from a function if it doesn’t have a meaningful result:

function myFunction(myArgument) {
  if (typeof myArgument === 'undefined') {
    return 'default';
  // handle the meaningful result

Comment if you have any doubts or suggestions on this Js undefined topic.

Note: The All JS Examples codes are tested on the Firefox browser and the Chrome browser.

OS: Windows 10

Code: HTML 5 Version

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