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w3schools.com › typescript › typescript_null.php

TypeScript Null & Undefined

Optional chaining is a JavaScript feature that works well with TypeScript's null handling. It allows accessing properties on an object that may or may not exist, using compact syntax. It can be used with the ?. operator when accessing properties. interface House { sqft: number; yard?: { sqft: number; }; } function printYardSize(house: House) { const yardSize = house.yard?.sqft; if (yardSize === undefined) { console.log('No yard'); } else { console.log(`Yard is ${yardSize} sqft`); } } let home: House = { sqft: 500 }; printYardSize(home); // Prints 'No yard' Try it Yourself »

w3schools.com › js › js_datatypes.asp

JavaScript Data Types

This is a historical quirk in JavaScript and does not indicate that null is an object. The strict equality operator (===) compares both the value and the type of the operands. It returns true only if both the operands values and types are null. The loose equality operator (==) also returns true for a null value, but it also returns true if the value is undefined. Using == is not recommended when checking for null. ... If you want to use W3Schools ...

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w3schools.com › js › js_typeof.asp

JavaScript typeof

In JavaScript null is "nothing".

w3schools.invisionzone.com › browser scripting › javascript

Affect of NULL Type in Coding - JavaScript - W3Schools Forum

November 1, 2016 - Having NULL type as an object to be a bug in js, is there any harm to code this could result in, and what precautions should we take to avoid such harm?

w3schools.com › jsref › jsref_oper_nullish.asp

JavaScript Nullish Coalescing Operator

Logical AND Logical OR Logical NOT Logical Nullish JS Bitwise Operators · Bitwise AND Bitwise OR Bitwise NOT Bitwise XOR Bitwise Left Bitwise Right Bitwise Signed JS Misc Operators · : ?. ... () ? x : y => delete in instanceof typeof void JS Precedence JS Promises

developer.mozilla.org › en-US › docs › Web › JavaScript › Reference › Operators › null

null - JavaScript | MDN

JavaScript is unique to have two nullish values: null and undefined. Semantically, their difference is very minor: undefined represents the absence of a value, while null represents the absence of an object. For example, the end of the prototype chain is null because the prototype chain is ...

w3schools.invisionzone.com › browser scripting › javascript

isEmpty() || === '' || === null -> not working? - JavaScript - W3Schools Forum

August 29, 2017 - Dear W3schools community, I want to check if a required input is empty (has more then 0 characters). You guys have any idea what I'm doing wrong? Thanks in advance! If there is no character in input (id="vname") I still get a red "bar" Here's my code: function foobar() { var vname = document.getE...

geeksforgeeks.org › javascript › null-in-javascript

Null in JavaScript - GeeksforGeeks

June 5, 2024 - In JavaScript, `null` indicates the deliberate absence of any object value. It's a primitive value that denotes the absence of a value or serves as a placeholder for an object that isn't present.

w3schools.blog › home › difference between undefined value and null value

Difference between undefined value and null value - W3schools

April 24, 2018 - A value that is not defined and has no keyword is known as an undefined value whereas a null value is explicitly specified by the keyword “null”.

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programiz.com › javascript › null-undefined

JavaScript null and undefined

In this tutorial, you will learn about null and undefined data types available in JavaScript with the help of examples.

sololearn.com › en › Discuss › 1731423 › how-to-check-null-valuesolved

How to check null value?[SOLVED] | Sololearn: Learn to code for FREE!

The easiest way is: var val = prompt('Hello'); if(val){ alert('Not null'); } else { alert('Null'); } This code works because if the input value is empty, it converts to boolean false. Otherwise it converts to boolean true.

w3schools.com › js › tryit.asp

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masteringjs.io › tutorials › fundamentals › null

`null` in JavaScript - Mastering JS

v == null; // Equivalent: v === null || v === undefined; The JavaScript language spec explicitly defines null as a value that represents the intentional absence of any object value.

stackoverflow.com › questions › 6003884 › how-do-i-check-for-null-values-in-javascript

How do I check for null values in JavaScript? - Stack Overflow

JavaScript is very flexible with regards to checking for "null" values. I'm guessing you're actually looking for empty strings, in which case this simpler code will work:

if(!pass || !cpass || !email || !cemail || !user){

Which will check for empty strings (""), null, undefined, false and the numbers 0 and NaN.

Please note that if you are specifically checking for numbers, it is a common mistake to miss 0 with this method, and num !== 0 is preferred (or num !== -1 or ~num (hacky code that also checks against -1)) for functions that return -1, e.g. indexOf).

To check for null SPECIFICALLY you would use this:

if (variable === null)

This test will ONLY pass for null and will not pass for "", undefined, false, 0, or NaN.

Additionally, I've provided absolute checks for each "false-like" value (one that would return true for !variable).

Note, for some of the absolute checks, you will need to implement use of the absolutely equals: === and typeof.

I've created a JSFiddle here to show all of the individual tests working

Here is the output of each check:

Null Test:

if (variable === null)

- variable = ""; (false) typeof variable = string

- variable = null; (true) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number



Empty String Test:

if (variable === '')

- variable = ''; (true) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number




Undefined Test:

if (typeof variable == "undefined")

-- or --

if (variable === undefined)

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (true) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number



False Test:

if (variable === false)

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (true) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (false) typeof variable = number



Zero Test:

if (variable === 0)

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (true) typeof variable = number

- variable = NaN; (false) typeof variable = number



NaN Test:

if (typeof variable == 'number' && !parseFloat(variable) && variable !== 0)

-- or --

if (isNaN(variable))

- variable = ''; (false) typeof variable = string

- variable = null; (false) typeof variable = object

- variable = undefined; (false) typeof variable = undefined

- variable = false; (false) typeof variable = boolean

- variable = 0; (false) typeof variable = number

- variable = NaN; (true) typeof variable = number

As you can see, it's a little more difficult to test against NaN;

Dmitri Pavlutin

dmitripavlutin.com › javascript-null

Everything about null in JavaScript

In this post, you'll learn everything about null in JavaScript: its meaning, how to detect it, the difference between null and undefined, and why using null extensively creates code maintenance difficulties.

shecodes.io › athena › 142857-understanding-the-values-null-and-undefined-in-javascript

[JavaScript] - Understanding the values null and undefined in JavaScript

Learn the meaning of null and undefined in JavaScript and how they are used to represent the absence of a value.

TutorialsTeacher

tutorialsteacher.com › javascript › javascript-null-and-undefined

Difference between null and undefined in JavaScript

A variable is undefined when you haven't assigned any value yet, not even a null.

web.dev › learn › javascript › data-types › null-undefined

null and undefined | web.dev

Learn how to use JavaScript's `null` and `undefined` data types.

w3schools.com › jsref › jsref_operators.asp

JavaScript Operators Reference

Logical AND Logical OR Logical NOT Logical Nullish JS Bitwise Operators · Bitwise AND Bitwise OR Bitwise NOT Bitwise XOR Bitwise Left Bitwise Right Bitwise Signed JS Misc Operators · : ?. ... () ? x : y => delete in instanceof typeof void JS Precedence JS Promises

tutorialspoint.com › What-is-the-difference-between-null-and-undefined-in-JavaScript

What is the difference between null and undefined in JavaScript?

In JavaScript, use null to explicitly indicate that a variable has no value or is intentionally empty. Use undefined when something is naturally missing, such as an uninitialized variable or a non-existing object property.