JavaScript - The Definitive Guide 7th Edition
1. ES6 was released in 2015 and added major new features - including class and module syntax. Since ES6, the EMCAScript has moved to a yearly release ES2016, ES2017 ...
2. Install Node and run node snippet.js
Console.log("Hello World");
or hello.html <script src="hello.js"></script>
3. let book = {
topic: "JavaScript",
edition: 7
};
book.topic
book["edition"] //another way to access property values
book.author="Flanagan";//create new properties
book.contents?.ch01?.set //conditionally access (ES2020)
4. In ES6 and laster, arrow function
const plus1 = x=>x+1;
5. Semicolons are optional
6. In ES6 and later, string literals can be delimited with backticks:
let name = "Bill";
let greeting = `Hello ${name}`;
7. In ES6 and later use let and const
8. a??b->(A!==null&&a!==undefined)?a:b
9. let a = [1,2,3]
let b = [0,...a,4];
10. let data = [1,2,3,4,5], sum = 0;
data.forEach(value=>{sum+=value;});
data.forEach(function(v,i,a){a[i]=v+1;}); //data=[2,3,4,5,6]
11. let a = [1,2,3];
a.map(x=>x*x) //[1,4,9]
12. let a = [1,2,3,4,5];
a.reduce( (x,y)=>x+y,0) //15, sum
a.reduce( (x,y)=>X*y,1) //120, product
the second argument is optional, init value to the funciton
13.
[1,[2,3]].flat() // [1,2,3]
[1,[2,[3]].flat() //[1,2,[3]]
14. a.flatMap(f)=>a.map(f).flat()
let phrases = ["Hello world","The Guide"];
let words = phrases.flatMap( phrases=>phrases.split(" ")); //["Hello","world","The","Guide"]
15. let a = [1,2,3];
a.join(" ") //"1 2 3"
16. f.call(o);
f.apply(o);
To invoke a function f as a method of the object o. apply() is like call, except that the arguments to be passed to the function are specified as an array: f.apply(0,[1,2]);
17. In Node, each file is an independent module with a private namespace.
Node modules import other modules with the require() function.
const fs = require("fs");
18. ES6 Exports
export const PI = Math.PI;
export function degreesToRadias(d){return d*PI/180;}
ES6 Imports
import BitSet from './bitset.js';
19. Promise (from ES6)
getJSON("/api/user/profile").then(displayUserProfile,handleProfileError);
if getJSON runs normally, it pases its result to displayUserProfile
if there is an error, then it passes an Error object to handleProfileError
getJSON("/api/user/profile").then(displayUserProfile).catch(handleProfileError);
any error in getJSON or in displayUserProfile, get passed to handleProfileError
queryDatabase().catch(e=>wait(500).then(queryDatabase))
.then(displayTable)
.catch(displayDatabaseError);
20.
let [value1,value2]=await Promise.all(getJSON(url1),getJSON(url2)];
21.
If you don't want your node program to completely crash.
process.setUncaughtExceptionCaptureCallback( error=>{
