check undefined in javascript

Checking for undefined in JavaScript is a crucial part of the broader best practices of coding in this language. This guide aims to break down the process of checking for undefined variables in JavaScript, ensuring smooth functioning of your code.

Code snippet for checking undefined in JavaScript

let myVariable;

if (typeof myVariable === 'undefined') {
    // handle the case where the variable is undefined
    console.log('Variable is undefined!');
} else {
    console.log('Variable is defined!');
}

Code Explanation for checking undefined in JavaScript

The code given above provides a blueprint for detecting whether a specified variable is undefined or not in JavaScript.

In the given code snippet, we start by declaring a variable called ‘myVariable’, but we do not assign any value to it, implying it is ‘undefined’.

The ‘if’ statement is then implemented, using the typeof operator to return a string that indicates the type of the operand.

In the case where ‘myVariable’ is undefined, the ‘typeof myVariable’ will return a string ‘undefined’. Therefore, the condition checked inside the ‘if’ statement, i.e., ‘typeof myVariable === ‘undefined” becomes true as the type of ‘myVariable’ is indeed ‘undefined’.

Consequently, the code within the ‘if’ block is executed, logging ‘Variable is undefined!’ into the console.

Conversely, if ‘myVariable’ had a value, the condition inside the ‘if’ statement would become false, and the code inside the ‘else’ block would be executed, logging ‘Variable is defined!’ onto the console.

This concise bit of JavaScript code allows developers to manage their code more effectively and avoid unexpected bugs by actively identifying and handling undefined variables.