How Can I Determine If a Variable Is ‘undefined’ or ‘null’?

When working with JavaScript, it is important to be able to determine if a variable is ‘undefined’ or ‘null’. This can be useful for handling different scenarios and avoiding errors in your code. In this blog post, we will explore different ways to check if a variable is ‘undefined’ or ‘null’.

Using the typeof Operator

The typeof operator in JavaScript returns a string indicating the type of a variable. When a variable is ‘undefined’, the typeof operator will return the string ‘undefined’. When a variable is ‘null’, the typeof operator will return the string ‘object’.

// Example variable declarations
var undefinedVariable;
var nullVariable = null;

// Using the typeof operator to check if a variable is 'undefined'
if (typeof undefinedVariable === 'undefined') {
  console.log('The variable is undefined');
}

// Using the typeof operator to check if a variable is 'null'
if (typeof nullVariable === 'object' && nullVariable === null) {
  console.log('The variable is null');
}

Using the strict equality operator (===)

The strict equality operator (===) in JavaScript compares both the value and the type of the variables being compared. When comparing a variable to ‘undefined’ or ‘null’ using the strict equality operator, it will return true only if the variable is exactly ‘undefined’ or ‘null’.

// Example variable declarations
var undefinedVariable;
var nullVariable = null;

// Using the strict equality operator to check if a variable is 'undefined'
if (undefinedVariable === undefined) {
  console.log('The variable is undefined');
}

// Using the strict equality operator to check if a variable is 'null'
if (nullVariable === null) {
  console.log('The variable is null');
}

Using the double equality operator (==)

The double equality operator (==) in JavaScript compares the value of the variables being compared, without considering their types. When comparing a variable to ‘undefined’ or ‘null’ using the double equality operator, it will return true if the variable is ‘undefined’ or ‘null’, but it may also return true for other falsy values such as an empty string (”), 0, or false.

// Example variable declarations
var undefinedVariable;
var nullVariable = null;

// Using the double equality operator to check if a variable is 'undefined'
if (undefinedVariable == undefined) {
  console.log('The variable is undefined');
}

// Using the double equality operator to check if a variable is 'null'
if (nullVariable == null) {
  console.log('The variable is null');
}

These are three different ways to determine if a variable is ‘undefined’ or ‘null’ in JavaScript. Choose the method that best suits your needs and the specific scenario you are working on.