Check if a variable is a string using JavaScript

In this article, we will check if a variable is a string using JavaScript. We can check the variable by using many methods. Checking the type of a variable can be done by using the typeof operator. It directly applies either to a variable name or to a variable.

Below are the following methods through which we can check the type of variable is a string:

• Using typeOf
• Using Instanceof Operator
• Underscore.js _.isString()

Approach 1: Using typeOf

Syntax:

typeof varName;

• varName: It is the name of the variable.

Example: This Example checks if the variable boolValue and numValue is a string. 

Javascript

let boolValue = true;
let numValue = 17;
let bool, num;

if (typeof boolValue == "string") {
    bool = "is a string";
} else {
    bool = "is not a string";
}
if (typeof numValue == "string") {
    num = "is a string";
} else {
    num = "is not a string";
}
console.log(bool);
console.log(num);

Output

is not a string
is not a string

Approach 2: Using Instanceof Operator

The instanceof operator in JavaScript is used to check the type of an object at run time.

Syntax:

let gfg = objectName instanceof objectType

Example:

Javascript

let variable = new String();

if (variable instanceof String) {
  console.log("variable is a string.");
} else {
  console.log("variable is not a string.");
}

Output

variable is a string.

Approach 3: Underscore.js _.isString()

The _.isString() function is used to check whether the given object element is string or not.

Syntax:

_.isString( object )

Example:

Javascript

let info = {
    Company: 'GeeksforGeeks',
    Address: 'Noida',
    Contact: '+91 9876543210'
};
console.log(_.isString(info));

let str = 'GeeksforGeeks';
console.log(_.isString(str));

Output:

false
true