What is “Falsy” in JavaScript? – onlinecode

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What is “Falsy” in JavaScript? – onlinecode

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In JavaScript, a value is falsy if JavaScript’s built-in type coercion converts it to false. For example, consider the below if statement:

if (v) {
  console.log('v is not falsy');
}

The console.log() will only run if v is not one of the below values:

false
0n: 0 as a BigInt
'': Empty string
null
undefined
NaN

These 7 values are the only falsy values in JavaScript. Any value that is not falsy is truthy.

In particular, a non-null object is always truthy, even if its valueOf() function returns a falsy value.

function isFalsy(v) {
  return !v;
}

// 'false'. The object form of '0' is truthy, even though 0 is falsy.
isFalsy(new Number(0));

Recommendations for What is “Falsy” in JavaScript

Using truthy/falsy for implicit type coercions in if statements is
typically messy. It is rare to find a case that the 7 falsy values are exactly
the set of values that you want to look out for.

For example, suppose you’re implementing a function that checks that a string
is shorter than 25 characters.

function checkLength(v) {
  if (!v) {
    throw new Error('Must provide a string!');
  }
  return v.length < 25;
}

Unfortunately, checkLength('') will throw an error because empty string is
falsy. Instead, you should check if v is a string:

function checkLength(v) {
  if (typeof v !== 'string') {
    throw new Error('Must provide a string!');
  }
  return v.length < 25;
}

Nullish Values for What is “Falsy” in JavaScript

Instead of checking for truthy/falsy values, you usually want to check for
“nullish” values. One of the common use cases for falsy checks is making sure
that you don’t get a TypeError: Cannot read property 'prop' of null error
when accessing a property of a value v.

It is it is safe to access v.prop unless v is strictly equal to null or
undefined. Even NaN.prop is fine.

const x = Number('abc');
x; // NaN
x.prop; // undefined

Checking if v == null is equivalent to v === null || v === undefined.
In other words, a value is loosely equal to null only if it is strictly
equal to null or undefined. So checking if v == null is often
more accurate than checking for truthy or falsy values.

JavaScript Fundamentals for What is “Falsy” in JavaScript

JavaScript is a programming language that is used to create interactive web pages. It is a client-side scripting language, which means that it runs on the user’s browser. JavaScript can be used to add animation, interactivity, and functionality to web pages.

Here are some of the fundamentals of JavaScript:

Variables: Variables are used to store data. They are declared using the var keyword.
Data types: JavaScript has a variety of data types, including strings, numbers, booleans, objects, and arrays.
Operators: Operators are used to perform operations on data.
Control flow statements: Control flow statements allow you to control the order in which your code is executed.
Functions: Functions are blocks of code that can be reused.
Objects: Objects are used to store data in key-value pairs.
Arrays: Arrays are used to store data in a sequential order.
Events and event handlers: Events are notifications that are sent by the browser when something happens, such as when the user clicks on an element or moves the mouse over an element. Event handlers are functions that are called in response to an event.
DOM manipulation: The Document Object Model (DOM) is a tree-like structure that represents the elements of a web page. JavaScript can be used to manipulate the DOM to change the appearance or behavior of a web page.

These are just some of the fundamentals of JavaScript. There are many other concepts that you can learn as you continue to develop your skills.

Here are some resources that you can use to learn more about JavaScript:

Mozilla Developer Network (MDN): The MDN is a great resource for learning about JavaScript. It has a comprehensive reference guide, tutorials, and articles on a wide range of topics.
W3Schools: W3Schools is another great resource for learning about JavaScript. It has interactive tutorials and quizzes that can help you learn the basics of the language.
JavaScript.info: JavaScript.info is a website that provides in-depth tutorials on JavaScript. It also has a forum where you can ask questions and get help from other JavaScript developers.

I hope this helps with What is “Falsy” in JavaScript!

Here are some additional tips for learning JavaScript:

Start with the basics: Before you start trying to build complex applications, it’s important to learn the basics of JavaScript. This includes things like variables, data types, operators, and control flow statements.
Practice regularly: The best way to learn JavaScript is to practice regularly. Try to find some time each day to work on JavaScript projects.
Get help from others: If you get stuck, don’t be afraid to ask for help from others. There are many online forums and communities where you can get help from other JavaScript developers.

With a little practice, you’ll be able to learn JavaScript and start building amazing web applications.

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