- Web Development with MongoDB and Node(Third Edition)
- Bruno Joseph D'mello Mithun Satheesh Jason Krol
- 389字
- 2021-07-08 10:32:44
Operators and flows
JavaScript supports similar control structures to other languages in the C family. Conditional statements are written with if and else, and you can chain together the statements using else-if ladders.
var a = "some value"; if(a === "other value") { //do something } else if (a === "another value") { //do something } else { //do something }
Control statements can be written using while, do-while, for, and switch statements. One important thing to consider while writing conditions in JavaScript is to understand what equates to true and/or false. Any value greater or less than zero, not null, and not undefined equates to true. Strings such as 0, null, undefined, or empty strings equate to false.
Some sample examples using while, do-while, for, and switch statements are as follows:
// for loop example var myVar = 0; for(let i = 0; i < 100; i += 1) { myVar = i; console.log(myVar); // => 0 1 ... 99 } // do while example var x = 0; do { x += 1; console.log(x); // => 1 2 ... 100 } while (x < 100); // while example while (x > 90) { x -= 1; console.log(x); // => 99 98 ... 90 } //switch example var x = 0; switch(x) { case 1 : console.log(""one""); break; case 2 : console.log("two""); break; default: console.log("none"); } // => "none"
Another important thing will be to understand the basic difference between
the comparisons using == and ===. The == comparisons should be used where
the type of variable is not your concern; and if the data type of the variables also should be compared, then you should opt for a === comparison symbol as given in the following code:
const a = '5'; const b = 5; if(a == b) { //do something } if(a === b) { //do something }
Here in the code snippet, the first condition evaluates to true while the second doesn't. So while you code, it's always safer to depend on strict (===) equality checks as a best practice.
- Angular UI Development with PrimeNG
- 零基礎學C++程序設計
- MATLAB圖像處理超級學習手冊
- HTML5 Mobile Development Cookbook
- 機械工程師Python編程:入門、實戰與進階
- JavaScript+Vue+React全程實例
- C程序設計案例教程
- Mastering JBoss Enterprise Application Platform 7
- Hands-On Automation Testing with Java for Beginners
- PLC應用技術(三菱FX2N系列)
- HoloLens與混合現實開發
- Building Serverless Architectures
- Mastering Concurrency in Python
- Java Web開發基礎與案例教程
- DevOps 精要:業務視角