What is the best way to check the type of a variable in JavaScript?

General Discussions
#1

What is the best way to check the type of a variable in JavaScript?

In the following code snippet:

function saveName(firstName) {
function capitalizeName() {
return firstName.toUpperCase();
}
var capitalized = capitalizeName();
console.log(capitalized instanceof String); // This shows false
return capitalized; }
console.log(saveName("Robert")); // Returns "ROBERT"

I want to check the type of the capitalized variable using capitalized instanceof String, but it returns false. I don’t want to use capitalized instanceof Function or Object, as that would take too much time.

What is the best way to JavaScript check type?

#2

Hi,

The simplest way to check the type of a variable is by using the typeof operator. It returns a string that represents the type of the unevaluated operand. In your case, you can check the type of capitalized like this:

var typeOfCapitalized = typeof capitalized;
console.log(typeOfCapitalized); // Output: "string"

This method is quick and easy, making it a great choice for javascript check type.

#3

Another method to check if a variable is specifically a string is to compare it directly with the string constructor. This will also work for string literals and string variables:

var isString = capitalized.constructor === String;
console.log(isString); // Output: true

Using this approach provides a clear way to javascript check type while ensuring you’re checking against the String constructor.

#4

If you need to perform a more comprehensive type check, you can use the Object.prototype.toString.call() method.

This method returns the exact type of the variable:

var typeOfCapitalized = Object.prototype.toString.call(capitalized);
console.log(typeOfCapitalized); // Output: "[object String]"

By utilizing this method, you can achieve a precise javascript check type that can differentiate between various types, including distinguishing strings from other types like objects.