Sharing tips on && and || expressions in javascript_javascript tips
If you are a newbie, and after reading the detailed explanation of all these techniques and how each technique works and then applying them, you will write more concise and efficient JavaScript programs.
Indeed, JavaScript masters have used these techniques to write many powerful and efficient JavaScript programs. But you can do this.
Powerful && and || expressions
You may have seen them in JavaScript libraries and JavaScript frameworks, so let’s start with a few basic examples:
Example 1. || (or)
Set default value, usually use
function documentTitle(theTitle) {
if (!theTitle) {
theTitle = "Untitled Document";
}
}
Replace this with:
function documentTitle(theTitle) {
theTitle = theTitle || "Untitled Document";
}
Analysis:
First, read the following "Tips" box to review how JavaScript determines Boolean values
The || operator first judges the truth or falsehood of the expression from the left. If it is true, it immediately returns the value returned by the expression on the left; if the expression on the left is judged as false, it continues to judge the expression on the right and returns the expression on the right. The value of
If theTitle is evaluated to be false, the value of the expression on the right will be returned. In other words, if theTitle variable is evaluated to be true, the value of theTitle will be returned.
! Tip:
Values judged as false by JavaScript: null, false, 0, undefined, NaN and "" (empty string).
Remember that NaN values like Infinity are evaluated as true and not false. However, NaN is evaluated as false.
Except for the above, all other values are judged to be true.
Example 2. && (and)
Don’t do this:
function isAdult(age) { if (age && age > 17) { return true; } else { return false; } }
Replace this with:
function isAdult(age) {
return age && age > 17;
}
Analysis:
The&& operator evaluates expressions from the left. If the expression on the left is evaluated as false, it immediately returns false, regardless of whether the expression on the right is true.
If the expression on the left is true, continue to evaluate the expression on the right, and then return the result of the expression on the right
This is getting fun
Example 3.
Don’t do this:
if (userName) { logIn(userName); } else { signUp(); }
Replace this with:
userName && logIn(userName) || signUp();
Analysis:
If userName is true, call the logIn function and pass the userName variable
If userName is false, call the logIn function without passing any variables
Example 4.
Don’t do this:
var userID; if (userName && userName.loggedIn) { userID = userName.id; } else { userID = null; }
Replace this with:
var userID = userName && userName.loggedIn && userName.id;
Analysis:
If userName is true, call user.loggedIn and check whether user.loggedIn is true; if it returns true, return the return value of the third expression
If userName is empty, return null
The above is the first JavaScript tip shared with you in this article. I hope you will like it.

Hot AI Tools

Undresser.AI Undress
AI-powered app for creating realistic nude photos

AI Clothes Remover
Online AI tool for removing clothes from photos.

Undress AI Tool
Undress images for free

Clothoff.io
AI clothes remover

Video Face Swap
Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Article

Hot Tools

Notepad++7.3.1
Easy-to-use and free code editor

SublimeText3 Chinese version
Chinese version, very easy to use

Zend Studio 13.0.1
Powerful PHP integrated development environment

Dreamweaver CS6
Visual web development tools

SublimeText3 Mac version
God-level code editing software (SublimeText3)

Hot Topics



Frequently Asked Questions and Solutions for Front-end Thermal Paper Ticket Printing In Front-end Development, Ticket Printing is a common requirement. However, many developers are implementing...

There is no absolute salary for Python and JavaScript developers, depending on skills and industry needs. 1. Python may be paid more in data science and machine learning. 2. JavaScript has great demand in front-end and full-stack development, and its salary is also considerable. 3. Influencing factors include experience, geographical location, company size and specific skills.

JavaScript is the cornerstone of modern web development, and its main functions include event-driven programming, dynamic content generation and asynchronous programming. 1) Event-driven programming allows web pages to change dynamically according to user operations. 2) Dynamic content generation allows page content to be adjusted according to conditions. 3) Asynchronous programming ensures that the user interface is not blocked. JavaScript is widely used in web interaction, single-page application and server-side development, greatly improving the flexibility of user experience and cross-platform development.

How to merge array elements with the same ID into one object in JavaScript? When processing data, we often encounter the need to have the same ID...

In-depth discussion of the root causes of the difference in console.log output. This article will analyze the differences in the output results of console.log function in a piece of code and explain the reasons behind it. �...

Discussion on the realization of parallax scrolling and element animation effects in this article will explore how to achieve similar to Shiseido official website (https://www.shiseido.co.jp/sb/wonderland/)...

Learning JavaScript is not difficult, but it is challenging. 1) Understand basic concepts such as variables, data types, functions, etc. 2) Master asynchronous programming and implement it through event loops. 3) Use DOM operations and Promise to handle asynchronous requests. 4) Avoid common mistakes and use debugging techniques. 5) Optimize performance and follow best practices.

Explore the implementation of panel drag and drop adjustment function similar to VSCode in the front-end. In front-end development, how to implement VSCode similar to VSCode...
