Js c1 best practices
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The document provides best practices for JavaScript coding including: 1. Using semicolons and curly braces with if/else statements, declaring local variables with the var keyword to avoid globals, and placing declarations at the top. 2. Initializing and using meaningful variable names, being aware of automatic type conversions between numbers and strings, and using === instead of == for comparisons. 3. Placing script tags at the bottom of pages, ending switch statements with default cases, and listing advantages of web applications like accessibility and regular updates. It also lists don'ts such as accidentally using the assignment operator, confusing addition and concatenation, breaking strings, ending array/object definitions with commas, and treating
![Initialize & meaningful variables
// Declare and initiate at the beginning
var firstName = "",
lastName = "",
price = 0,
discount = 0,
fullPrice = 0,
myArray = [],
myObject = {};](https://image.slidesharecdn.com/jsc1bestpractices-160912173313/85/Js-c1-best-practices-5-320.jpg)
![Ending an Array & Object Definition
with a Comma
points = [40, 100, 1, 5, 25, 10,];
person = {firstName:"John", lastName:"Doe", age:46,}](https://image.slidesharecdn.com/jsc1bestpractices-160912173313/85/Js-c1-best-practices-17-320.jpg)
Js c1 best practices
- 2. Use “;” & Curly Braces if(someVariable) x = false ---------------------------------------------------------------------------------------- if(someVariable) { x = false; } anotherFunction();
- 3. Always Declare Local Variables ¤ All variables used in a function should be declared as local variables. ¤ Local variables must be declared with the var keyword, otherwise they will become global variables. Declarations on Top
- 4. Avoid Global Variables ¤ Global variables and functions can be overwritten by other scripts. ¤ Use local variables instead, and learn how to use closures. Declarations on Top
- 5. Initialize & meaningful variables // Declare and initiate at the beginning var firstName = "", lastName = "", price = 0, discount = 0, fullPrice = 0, myArray = [], myObject = {};
- 6. Beware of Automatic Type Conversions var x = "Hello"; // typeof x is a string x = 5; // changes typeof x to a number ---------------------------------------------------------------------------------------- var x = 5 + 7; // x.valueOf() is 12, typeof x is a number var x = 5 + "7"; // x.valueOf() is 57, typeof x is a string
- 7. Beware of Automatic Type Conversions var x = "5" + 7; // x.valueOf() is 57, typeof x is a string var x = 5 - 7; // x.valueOf() is -2, typeof x is a number var x = 5 - "7"; // x.valueOf() is -2, typeof x is a number var x = "5" - 7; // x.valueOf() is -2, typeof x is a number var x = 5 - "x"; // x.valueOf() is NaN, typeof x is a number
- 8. Comparisons “==” vs “===” ¤ The == operator will compare for equality after doing any necessary type conversions (to matching types). ¤ The === operator forces comparison of values and type ---------------------------------------------------------------------------------------- 0 === ""; // false 1 === "1"; // false 1 === true; // false 0 == ""; // true 1 == "1"; // true 1 == true; // true
- 9. Place Scripts at the Bottom Page <p>And you don’t know JS yet. </p> <script type="text/javascript" src="path/to/file.js"></script> <script type="text/javascript" src="path/to/ anotherFile.js"></script> </body> </html>
- 10. End Switches with Defaults switch (new Date().getDay()) { case 0: day = "Sunday"; break; case 1: day = "Monday"; break; default: day = "Unknown"; }
- 11. Advantages
- 12. Advantages ¤ There is no need to install the application on each machine. ¤ New versions of software can be released on a regular basis without needing users to follow an upgrade process. In fact some web applications have daily releases of software. ¤ Web applications can be hosted on cloud based infrastructure, leading to higher availability, and lower costs. ¤ The same web application can be used on multiple devices, including handheld devices” ¤ Fragmento de: Dane Cameron. “A Software Engineer Learns HTML5, JavaScript and jQuery: A guide to standards-based web applications”. iBooks.
- 13. Dont’s
- 14. Accidentally Using the Assignment Operator var x = 0; 1. if (x == 10) 2. if (x = 10) 3. If (x = 0)
- 15. Confusing Addition & Concatenation var x = 10 + 5; // the result in x is 15 var x = 10 + "5"; // the result in x is "105"
- 16. Breaking a JavaScript String var x = "Hello World!"; _________________________________________________________ var x = "Hello World!";
- 17. Ending an Array & Object Definition with a Comma points = [40, 100, 1, 5, 25, 10,]; person = {firstName:"John", lastName:"Doe", age:46,}
- 18. Undefined is Not Null if (myObj !== null && typeof myObj !== "undefined") ¤ Correct if (typeof myObj !== "undefined" && myObj !== null)