How to check type in javascript?

Introduction

In JavaScript, checking the type of a value is a common task that developers encounter. Understanding the type of a value is crucial for writing robust and error-free code. This article will delve into the various methods available in JavaScript to check the type of a value, providing you with a comprehensive guide on how to perform type checks effectively.

Using the typeof operator

The simplest way to check the type of a value in JavaScript is by using the typeof operator. This operator returns a string indicating the type of the operand. For example, to check the type of a variable named “value”, you can use the following code:

“`
typeof value;
“`

The typeof operator returns one of the following string values:

– “undefined” if the value is undefined
– “boolean” if the value is a boolean
– “number” if the value is a number
– “string” if the value is a string
– “symbol” if the value is a symbol (added in ECMAScript 6)
– “object” if the value is an object or null
– “function” if the value is a function

It’s important to note that typeof null returns “object” instead of “null”, which is a historical quirk in JavaScript.

Using the instanceof operator

The instanceof operator allows you to check whether an object belongs to a specific class or constructor. It checks the prototype chain of an object, making it useful for checking the type of objects created from custom classes. Here’s an example:

“`
value instanceof Array;
“`

The instanceof operator returns true if the object is an instance of the specified class or constructor, and false otherwise.

Using the constructor property

Every JavaScript object has a constructor property that refers to the constructor function used to create the object. You can use this property to check the type of an object. Here’s an example:

“`
value.constructor === Array;
“`

This code checks if the constructor of the object referenced by “value” is the Array constructor. You can replace “Array” with any other constructor to check for different types.

Using the Object.prototype.toString() method

The Object.prototype.toString() method is a versatile way to check the type of a value in JavaScript. It returns a string representing the object’s type. Here’s an example:

“`
Object.prototype.toString.call(value);
“`

This code returns a string in the format “[object Type]”, where “Type” represents the type of the value. For example, “[object Array]” for an array, “[object Object]” for an object, and so on.

Conclusion

Checking the type of a value is an essential task in JavaScript development. By using the typeof operator, instanceof operator, constructor property, or Object.prototype.toString() method, you can accurately determine the type of a value and write more robust code. Remember to choose the appropriate method based on your specific use case.

References

– developer.mozilla.org
– w3schools.com
– ecma-international.org