Check if a variable is a string using JavaScript

Checking if a variable is a string in JavaScript is a common task to ensure that the data type of a variable is what you expect. This is particularly important when handling user inputs or working with dynamic data, where type validation helps prevent errors and ensures reliable code execution.

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

Using typeOf Operator

In this approach, we are using typeOf operator which tells us the type of the given value. we are getting the type of the value by the use of the typeOf operator and we are using if-else for returning our ans.

Example: This example shows the implementation of the above-explained approach.

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);

is not a string
is not a string

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: This example shows the implementation of above-explained appraoch.

let variable = new String();

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

variable is a string.

Underscore.js _.isString()

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

Syntax:

_.isString( object );

Example: This example shows the implementation of above-explained appraoch.

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

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

Output:

false
true

Using Lodash _.isString() Method

In this approach, we are using the Lodah _.isString() method that returns boolean response for the given value.

Example: This example shows the implementation of above-explained appraoch.

// Requiring the lodash library 
const _ = require("lodash");

// Use of _.isString() method 
console.log(_.isString('GeeksforGeeks'));
console.log(_.isString(true));

Output:

true
false

Using Object.prototype.toString.call Method

The Object.prototype.toString.call method is a reliable way to determine the type of a variable. It returns a string indicating the type of the object.

Syntax:

Object.prototype.toString.call(variable) === '[object String]'

Example: This example shows the implementation of the above-explained approach.

function checkIfString(variable) {
    if (Object.prototype.toString.call(variable) === '[object String]') {
        console.log("variable is a string.");
    } else {
        console.log("variable is not a string.");
    }
}

// Test cases
checkIfString("Hello, World!");  
checkIfString(42);               
checkIfString(true);             
checkIfString({});               
checkIfString(new String("Test")); 

variable is a string.
variable is not a string.
variable is not a string.
variable is not a string.
variable is a string.