Javascript number is null

Check if a Value Is Null or Undefined in JavaScript or Node.js

JavaScript uses two representations of „empty“ values. When „empty“ we mean that they don’t have an exact value assigned. These two values are null and undefined .

Both values, null and undefined , are valuable in JavaScript. Except when you are not checking for them. In such cases, you’re running into errors where you’re not able to access a property or method on “null” or “undefined”.

This tutorial shows you how to check whether a given value is either null or undefined .

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Detect Null or Undefined Values in JavaScript

You can create a utility method checking whether a given input is null and undefined . Here’s a sample function that you may copy to your project and is it to check for empty values:

/** * Determine whether the given `value` is `null` or `undefined`. * * @param value * * @returns */ function isNullOrUndefined (value) < return value == null // `value == null` is the same as `value === undefined || value === null` >

The value == null comparison is a handy way to check for null and undefined simultaneously. The loose equality operator attempts to convert and compare operands of different types.

Using the „@supercharge/goodies“ Package

I’m the maintainer of the @supercharge/goodies package providing convenient helper functions for Node.js and JavaScript. This package comes with a handy isNullish(value) method determining whether the given value is null or undefined :

const < isNullish >= require('@supercharge/goodies') isNullish(null) // true isNullish(undefined) // true isNullish(0) // false isNullish('') // false isNullish(<>) // false isNullish([]) // false isNullish(false) // false 

Notice: the isNullish method is fully typed and your code editor or IDE knows that the provided value is either null/undefined or not. The typing happens because the @supercharge/goodies package is written in TypeScript and provides proper typing for the isNullish method.

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Источник

How to Check null Values in JavaScript? | isNull() JavaScript

In this article we will learn how to check null values using JavaScript.

The null value represents the absence of any object value. It is one of the primitive value in JavaScript and is falsy for boolean operations.

In this article we will check one of the way to determine if a value is null or not.

Create isNull() function in JavaScript

In JavaScript we can create a function call isNull() which will check if a value is null or not.

function isNull(val)< if(val === null)< return true; > return false; > console.log(isNull(null)) // true console.log(isNull('')) // false console.log(isNull(0)) // false console.log(isNull(undefined)) //false console.log(isNull(NaN)) //false 

Why use === instead of == ?

The == (loose equality operator) performs some kinds of coercion. So, when we compare something like this

console.log(' ' == 0) // true console.log(undefined == null) // true 

The == operator says that both the comparison are true .

Now, if we do the same comparison with === (strict equality operator) we get the results as false .

console.log(' ' === 0) //false console.log(undefined === null) //false 

Therefore, we have used the === operator to get accurate results.

Using Lodash or Underscore.js _.isNull() Function

We can also use external JavaScript libraries like Lodash or Underscore to check for null values.

The library checks whether the value of the object is null or not. If the value is null it will return as true otherwise false .

console.log(_.isNull(10)) // false console.log(_.isNull(null)) //true 

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