Home Web Front-end JS Tutorial How to convert bool value in js?

How to convert bool value in js?

Jun 19, 2018 pm 02:04 PM
js

This article mainly introduces to you the conversion method of bool value in js and the related information of "&&", "||", "!!". The article introduces it in detail through sample code, which is very helpful for everyone's learning. Or the work has certain reference and learning value. Friends who need it can come and take a look below.

Preface

The first thing you need to know is that there are 6 values ​​​​in js that are false, namely: 0, '', null, undefined, NaN and false, others (including {}, [], Infinity) are true.

You can use the Boolean() function or negate twice to get the Boolean value of the object, such as Boolean(undefined ) and !!undefined can also obtain the Boolean value false,

For 0, '', null, undefined, NaN, {}, [], Infinity, the Boolean value is false false false false false true true true.

So one thing we know is: the Boolean value of an object is true, even if it is an object {}.

bool value conversion

##Data typebool value conversionundefinedundefined is converted to falseObjectnull is converted to false, Others are trueBooleanfalse is converted to false, true is converted to trueNumber 0, NaN is converted to false, others are trueString"" is converted to false, others are true

"&&"

The "&&" operator in JavaScript is as follows:

If && left If the value of the side expression is true, the value of the right side expression is returned; otherwise, the value of the left side expression is returned. When multiple && expressions are evaluated together, the value of the first expression that evaluates to false is returned. If all expressions evaluate to true, the value of the rightmost expression is returned.

const aa = {'name': 'xx'};
const bb = aa && aa.age; // bb输出为undefined;
let cc;
const dd = cc && cc.name ? cc.name : undefined; // dd输出为undefined
const dd = cc && cc.name; // dd输出为undefined;
Copy after login

The execution results of the above two sentences of code are the same. I have always used the above method when writing code before, but found that some single tests cannot be covered, resulting in a very low single test branch coverage. Change to the following This problem can be solved very well. The effect of these two sentences is the same.

"||"

The algorithm of "||" operator in javascript is as follows:

If the value of the expression on the left side of "||" is true, return the value of the expression on the left side; otherwise, return the value of the expression on the right side. When multiple "||" expressions are operated together, the value of the first expression is returned as true, if all expressions are evaluated as false, otherwise the value of the rightmost expression is returned.

const aa = false || 'xx'; // aa输出为'xx'
Copy after login

"!!"

"!!"Forcibly convert the expression into a bool value, and the result of the operation is true or false.

const aa = 'xx';
const bb = !!aa; // bb输出为true
const cc = !!(NaN || undefined || null || 0 || '' ); // cc为false;
Copy after login

The above is what I compiled for everyone. I hope it will be helpful to everyone in the future.

Related articles:

Implementing asynchronous update queue through nextTick() in Vuejs

How to implement 3D model in three.js Show

Angular CLI installation tutorial

How to implement Toast using ReactNative

How to do it using CommonsChunkPlugin Only by extracting public modules

There are complex operations about MVC in AngularJS

The above is the detailed content of How to convert bool value in js?. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Undress AI Tool

Undress AI Tool

Undress images for free

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

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

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

How to use JS and Baidu Maps to implement map pan function How to use JS and Baidu Maps to implement map pan function Nov 21, 2023 am 10:00 AM

How to use JS and Baidu Map to implement map pan function Baidu Map is a widely used map service platform, which is often used in web development to display geographical information, positioning and other functions. This article will introduce how to use JS and Baidu Map API to implement the map pan function, and provide specific code examples. 1. Preparation Before using Baidu Map API, you first need to apply for a developer account on Baidu Map Open Platform (http://lbsyun.baidu.com/) and create an application. Creation completed

Recommended: Excellent JS open source face detection and recognition project Recommended: Excellent JS open source face detection and recognition project Apr 03, 2024 am 11:55 AM

Face detection and recognition technology is already a relatively mature and widely used technology. Currently, the most widely used Internet application language is JS. Implementing face detection and recognition on the Web front-end has advantages and disadvantages compared to back-end face recognition. Advantages include reducing network interaction and real-time recognition, which greatly shortens user waiting time and improves user experience; disadvantages include: being limited by model size, the accuracy is also limited. How to use js to implement face detection on the web? In order to implement face recognition on the Web, you need to be familiar with related programming languages ​​and technologies, such as JavaScript, HTML, CSS, WebRTC, etc. At the same time, you also need to master relevant computer vision and artificial intelligence technologies. It is worth noting that due to the design of the Web side

How to create a stock candlestick chart using PHP and JS How to create a stock candlestick chart using PHP and JS Dec 17, 2023 am 08:08 AM

How to use PHP and JS to create a stock candle chart. A stock candle chart is a common technical analysis graphic in the stock market. It helps investors understand stocks more intuitively by drawing data such as the opening price, closing price, highest price and lowest price of the stock. price fluctuations. This article will teach you how to create stock candle charts using PHP and JS, with specific code examples. 1. Preparation Before starting, we need to prepare the following environment: 1. A server running PHP 2. A browser that supports HTML5 and Canvas 3

Essential tools for stock analysis: Learn the steps to draw candle charts with PHP and JS Essential tools for stock analysis: Learn the steps to draw candle charts with PHP and JS Dec 17, 2023 pm 06:55 PM

Essential tools for stock analysis: Learn the steps to draw candle charts in PHP and JS. Specific code examples are required. With the rapid development of the Internet and technology, stock trading has become one of the important ways for many investors. Stock analysis is an important part of investor decision-making, and candle charts are widely used in technical analysis. Learning how to draw candle charts using PHP and JS will provide investors with more intuitive information to help them make better decisions. A candlestick chart is a technical chart that displays stock prices in the form of candlesticks. It shows the stock price

How to use JS and Baidu Map to implement map click event processing function How to use JS and Baidu Map to implement map click event processing function Nov 21, 2023 am 11:11 AM

Overview of how to use JS and Baidu Maps to implement map click event processing: In web development, it is often necessary to use map functions to display geographical location and geographical information. Click event processing on the map is a commonly used and important part of the map function. This article will introduce how to use JS and Baidu Map API to implement the click event processing function of the map, and give specific code examples. Steps: Import the API file of Baidu Map. First, import the file of Baidu Map API in the HTML file. This can be achieved through the following code:

How to use JS and Baidu Maps to implement map heat map function How to use JS and Baidu Maps to implement map heat map function Nov 21, 2023 am 09:33 AM

How to use JS and Baidu Maps to implement the map heat map function Introduction: With the rapid development of the Internet and mobile devices, maps have become a common application scenario. As a visual display method, heat maps can help us understand the distribution of data more intuitively. This article will introduce how to use JS and Baidu Map API to implement the map heat map function, and provide specific code examples. Preparation work: Before starting, you need to prepare the following items: a Baidu developer account, create an application, and obtain the corresponding AP

PHP and JS Development Tips: Master the Method of Drawing Stock Candle Charts PHP and JS Development Tips: Master the Method of Drawing Stock Candle Charts Dec 18, 2023 pm 03:39 PM

With the rapid development of Internet finance, stock investment has become the choice of more and more people. In stock trading, candle charts are a commonly used technical analysis method. It can show the changing trend of stock prices and help investors make more accurate decisions. This article will introduce the development skills of PHP and JS, lead readers to understand how to draw stock candle charts, and provide specific code examples. 1. Understanding Stock Candle Charts Before introducing how to draw stock candle charts, we first need to understand what a candle chart is. Candlestick charts were developed by the Japanese

The relationship between js and vue The relationship between js and vue Mar 11, 2024 pm 05:21 PM

The relationship between js and vue: 1. JS as the cornerstone of Web development; 2. The rise of Vue.js as a front-end framework; 3. The complementary relationship between JS and Vue; 4. The practical application of JS and Vue.

See all articles