Javascript check if value is a string

Check If Value Is a String in JavaScript: A Comprehensive Guide

Learn how to check if a value is a string in JavaScript with different methods like typeof operator, Object.prototype.toString.call(), Lodash/Underscore library, and more. Discover the best practices and choose the appropriate method for your specific use case.

As a developer, you may come across situations where you need to check if a value is a string in javascript . This can be useful when validating user input , performing string manipulations, or simply checking the type of a variable. In this comprehensive guide, we will explore the different methods that can be used to check if a value is a string in JavaScript.

I. Introduction

Checking if a value is a string is an important task in JavaScript development. It ensures that you are working with the correct data type and can prevent unexpected errors in your code. There are various methods that can be used to check if a value is a string, and each method has its own advantages and disadvantages.

In this guide, we will cover the most commonly used methods to check if a value is a string in JavaScript. We will explore the typeof operator, Object.prototype.toString.call() function, Lodash/Underscore library, and other methods that can be used to check if a value is a string.

II. Using typeof Operator to Check If a Variable Is a String in JavaScript

The typeof operator is a built-in JavaScript operator that returns the type of a variable. It can be used to check if a variable is a string by comparing its result to the string “string”.

let str = "Hello World!"; console.log(typeof str); // Output: "string" 

This code will output “string” because the typeof operator returns the string “string” when applied to a string variable.

Best Practices for Using typeof Operator

When using the typeof operator to check if a variable is a string , it is important to keep in mind the following best practices:

• Always use strict equality (===) when comparing the result of the typeof operator to the string “string”.
• Be aware that typeof null also returns “object”, so you may need to explicitly check for null values if you are using this method.

III. Using Object.prototype.toString.call() Function to Check If a Variable Is a String in JavaScript

The Object.prototype.toString.call() function is a built-in JavaScript function that can be used to get the internal [[Class]] property of an object. When applied to a string variable, it returns “[object String]”. This can be used to check if a variable is a string by comparing its result to the string “[object String]”.

let str = "Hello World!"; console.log(Object.prototype.toString.call(str)); // Output: "[object String]" 

This code will output “[object String]” because the Object.prototype.toString.call() function returns “[object String]” when applied to a string variable.

Comparison of Using typeof Operator and Object.prototype.toString.call() Function to Check If a Variable Is a String

Both typeof operator and Object.prototype.toString.call() function can be used to check if a variable is a string in javascript . However, there are some differences between the two methods.

The typeof operator only checks if the variable is a string, while Object.prototype.toString.call() function checks if the variable is an object with a [[Class]] property of “String”. This means that the latter method can be used to check if an object is a string as well.

Best Practices for Using Object.prototype.toString.call() Function

When using the Object.prototype.toString.call() function to check if a variable is a string, it is important to keep in mind the following best practices:

• Always compare the result of the Object.prototype.toString.call() function to the string “[object String]” using strict equality (===).
• Be aware that this method can be used to check if an object is a string as well.

IV. Using Lodash/Underscore Library to Check If a Variable Is a String in JavaScript

Lodash and Underscore are popular JavaScript utility libraries that provide a variety of useful functions for working with arrays, objects, and strings. One of the functions provided by these libraries is the _.isString() function, which can be used to check if a variable is a string.

let str = "Hello World!"; console.log(_.isString(str)); // Output: true 

This code will output “true” because the _.isString() function returns true when applied to a string variable.

Comparison of Using Lodash/Underscore Library and Other Methods to Check If a Variable Is a String

Using Lodash/Underscore library to check if a variable is a string has some advantages over other methods. The _.isString() function is easy to use, and it works with both primitive strings and string objects.

However, using Lodash/Underscore library to check if a variable is a string may not be the best option if you are not already using these libraries in your project.

Best Practices for Using Lodash/Underscore Library

When using Lodash/Underscore library to check if a variable is a string, it is important to keep in mind the following best practices:

• Make sure that you have included the library in your project before using any of its functions.
• Use the _.isString() function to check if a variable is a string.

V. Other Methods to Check If a Variable Is a String in JavaScript

In addition to the methods we have discussed so far, there are other methods that can be used to check if a variable is a string in JavaScript. These include:

isNaN() Method to Check If a String Is a Number

The isNaN() method is a built-in JavaScript function that returns true if the argument is not a number. This can be used to check if a string is a number by applying the function to the string and checking if it returns true.

let str = "123"; console.log(isNaN(str)); // Output: false 

This code will output “false” because the isNaN() function returns false when applied to the string “123”.

includes() Method to Determine Whether a String Contains the Given Characters or Not

The includes() method is a built-in JavaScript function that returns true if a string contains the specified characters. This can be used to check if a variable is a string by applying the function to the variable and checking if it returns true.

let str = "Hello World!"; console.log(str.includes("Hello")); // Output: true 

This code will output “true” because the includes() function returns true when applied to the string “Hello World!” and the substring “Hello”.

isInteger() Method to Check If a Value Is an Integer or Not

The isInteger() method is a built-in JavaScript function that returns true if the argument is an integer. This can be used to check if a string is an integer by applying the function to the string and checking if it returns true.

let str = "123"; console.log(Number.isInteger(parseInt(str))); // Output: true 

This code will output “true” because the parseInt() function converts the string “123” to the integer 123, and the Number.isInteger() function returns true when applied to the integer 123.

Comparison of Using Other Methods and Previously Mentioned Methods to Check If a Variable Is a String

The other methods we have discussed can also be used to check if a variable is a string in JavaScript. However, they may have some limitations or may not be as reliable as the previously mentioned methods.

Best Practices for Using Other Methods

When using other methods to check if a variable is a string in JavaScript, it is important to keep in mind the following best practices:

• Be aware of the limitations of each method and choose the appropriate method for your specific use case.
• Always test your code thoroughly to ensure that it is working as expected.

VI. Conclusion

In this comprehensive guide, we have explored the different methods that can be used to check if a value is a string in JavaScript. We have covered the typeof operator, Object.prototype.toString.call() function, Lodash/Underscore library, and other methods that can be used to check if a value is a string.

When choosing a method to check if a variable is a string, it is important to consider the specific use case and choose the appropriate method accordingly. By following the best practices outlined in this guide, you can ensure that your code is reliable and working as expected.

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JavaScript: Check if Variable Is a String

JavaScript supports a variety of data types such as strings, numbers, floats, etc. A string is a collection of characters such as «John Doe». Typically, you create them by enclosing characters in double or single quotes. Alternatively, you can make a string by using the new String() constructor:

let myString = 'John Doe'; let myString2 = new String("John Doe"); 

When performing specific operations, you may face a situation that demands you to verify that a specific variable is a string before processing it — lest an error be thrown. We’ll cover that situation in this article! First, we’ll take a look at how to check if a particular variable is a string in JavaScript and then show you an alternative approach that uses the Lodash library.

Standard Solution — Using typeof Operator

In JavaScript, the typeof operator is the most used method to check the type of any variable. Alternatively, you can use the typeof() method:

let myString = 'John Doe'; typeof myString; // string typeof(myString); // string 

If used with a string, the typeof operator returns «string» . Let’s create a simple example to confirm this:

let myString = "John Doe"; if (typeof myString === "string") < console.log("This variable is a string"); > else < console.log("This variable is not a string"); > 

Indeed, the myString is a string:

This variable is a string 

Note: Even if the variable contains a number that is wrapped in single/double quotes, it still would be considered a string.

One interesting problem with the typeof operator is that it doesn’t recognize strings created using the new String() constructor. The new keyword creates a new JavaScript object that is the instance of the String type. Therefore, the typeof operator won’t correctly recognize strings created using the new String() constructor:

let myString = new String('John Doe'); console.log(typeof myString); // "object" 

In this case, instead of the typeof operator, we need to use the instanceof operator — it can detect that the object created with the new String() constructor is the instance of the String type:

let myString = new String("John Doe"); if (myString instanceof String) < console.log("This variable is a string"); > else < console.log("This variable is not a string"); > 

Since the myString is a string, this code will produce the following output:

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This variable is a string 

Using Lodash Library

If you’re already using the Lodash library in your project, there’s no harm in using it for checking whether a variable is a string or not! It’s absolutely not necessary to have a dependency if we don’t need Lodash for something else, but, if we already have that dependency, we can make use of the _.isString() method, which returns true if the specified value is a string primitive or a String object, making it fit for both explicitly and implicitly created strings:

let myString = new String("John Doe"); if (_.isString(myString)) < console.log("This variable is a string"); > else < console.log("This variable is not a string"); > 

This variable is a string 

Conclusion

In this article, we’ve learned how to check if a variable is a string in JavaScript. Also, we’ve learned how this works with an external library like Lodash.

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