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Check if a variable is a string in JavaScript

Here, we'll discuss that how to check whether a variable is a string or not in JavaScript?
Submitted by Pratishtha Saxena, on May 24, 2022

A data type is said to be a string if it is a sequence of characters. It is the textual data stored in a variable. In JavaScript, it is defined within single or double quotes and also using a new String() constructor.

str1 = "This is my place."
str2 = 'That is your place.'
str3 = new String('Great Place');

Now to check whether a given variable is a string or not, we'll use a JavaScript operator called typeof.

Syntax:

typeof variable;

This operator returns the data type of the variable specified after it. If the variable is of string data type, it will return a string.

Alternatively, it can also be used as typeof() method in JavaScript.

Syntax:

typeof(variable);

Example 1:

str = "This is my place.";

if (typeof str == String) {
console.log('The variable is a String.');
} else {
console.log('The variable is not a String.');
}

Output:

The variable is not a String.

Example 2:

str = "That is your place.";

if (typeof(str) === 'string') {
	console.log('The variable is a String.');
} else {
	console.log('The variable is not a String.');
}

Output:

The variable is a String.

But, one of the drawbacks of using typeof() is that when it is applied to the variable declared by the new String() constructor, then instead of returning a string, its return object as its data type. Hence, it does not recognize the strings created in this way.

So, here instead of using typeof(), we'll use instanceof operator. This operator detects the strings created by the new String() constructor.

Syntax:

variable instanceof String;

The above expression will return true if the variable is String.

Example 3:

str = new String("My name is Tom.");

if (str instanceof String) {
	console.log('The variable is a String.');
} else {
	console.log('The variable is not a String.');
}

Output:

The variable is a String.

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