JavaScript Program To Check If A Variable Is undefined or null

JavaScript is a widely-used programming language for creating interactive web pages and applications. Variables are used to store data that can be accessed and modified later in JavaScript. Occasionally, however, these variables may be null or their value may be unknown. This can lead to code errors and cause the application to crash.

Therefore, it is essential to determine whether a variable has a value prior to using it. In this article, we will discuss how to determine if a JavaScript variable is undefined or null.

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Program To Check If A Variable Is undefined or null

In the code given below, a variable is checked if it is equivalent to null. The null with == checks for both null and undefined values. This is because null == undefined evaluates to true.

// JavaScript Program to check if a variable is undefined or null

function checkVariable(variable) {

    if(variable == null) 
        console.log('The variable is undefined or null');
    
    else 
       console.log('The variable is neither undefined nor null');
}

let newVariable;

checkVariable(50);
checkVariable(1.5);
checkVariable("JavaScript is the world's most popular programming language.");
checkVariable(null);
checkVariable(newVariable);

The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is undefined or null
The variable is undefined or null

Program To Check If A Variable Is undefined or null using typeof Operator

The typeof operator for undefined value returns undefined. Hence, you can check the undefined value using typeof operator. Also, null values are checked using the === operator. We cannot use the typeof operator for null as it returns an object.

// JavaScript Program to check if a variable is undefined or null

function checkVariable(variable) {

    if( typeof variable === 'undefined' || variable === null ) 
        console.log('The variable is undefined or null');
  
    else 
       console.log('The variable is neither undefined nor null');
}

let newVariable;

checkVariable(5);
checkVariable(1.5);
checkVariable("JavaScript is the world's most popular programming language.");
checkVariable(null);
checkVariable(newVariable);

The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is neither undefined nor null
The variable is undefined or null
The variable is undefined or null

Conclusion

In conclusion, it is necessary to determine whether a variable has a value before utilizing it in JavaScript. Errors in the code can be caused by undefined and null values, which can also cause the program to crash. In this article, we discussed how to use a hook and the typeof operator to determine whether a JavaScript variable is undefined or null.