Skip to content

Obsidian Arrow

Javascript Note

Javascript Note

About NodeJS see Node Note
@2021-12-24: Renamed ES6 Note to JS Note since ES next, es 2021, es2022

Overloading a built-in Class#

@2021-09-24
Classes are not just syntactic sugar for the prototypal pattern
JavaScript has no user-defined operator overloading
But the value get by valueOf() can be overloaded like this

Class inheritance#

@2021-10-04
class B extends A needs to call super() and the return value(constructed class instance) of A.constructor() is stored in B.this.

Online sandbox#

@2021-10-08
Stackblitz vs CodeSandbox
Stackblitz is much faster but the package can only be imported from its own NPM system.
CodeSandbox can add preview packages

Object.assign()#

@2021-10-21
will change first var.

Array Trap#

@2021-10-21
Trap: arr.entries() and arr.forEach() takes different (ind,val) order: [ind,val] in arr.entries() and arr.forEach((val,ind)=>null)

BigInt#

@2021-10-21
Is a primitive JS type
Has literal expression (BigInt(5) === 5n;)
Division will automatic floor.

String Template#

@2021-12-16
[ ] TODO : ruanyifeng

const FooterWrap = styled('div')({
color: 'red',
});

// const FooterWrap = styled('div')`
// color: red;
//`;

Typing and JSDocs#

@2021-12-21
Object arguments with param: Stack Overflow How to describe "object" arguments in jsdoc?, Official web @param.
TS ? optional operator is = in jsdoc.
Empty property type check: Property ... does not exist on type 'IntrinsicAttributes & ...': to solve JSX error , use |{}.

Tagged template#

@2021-12-18
Tagged template
Chinese version, Ruanyifeng, Tagged template

Proxy#

@2021-12-28
How to use javascript proxy for nested objects : Use two proxies
@2021-01-03
array.push will not trigger "set" method of proxy
Example on Gist

Throw Error#

@2022-01-03
throw Error('msg') and throw new Error('msg') does the same thing. Because Error('msg') and new Error('msg') are the same thing.
Full answer on Stack Overflow

Import and Export#

@2022-01-10
import '/modules/my-module.js' will Import a module for its side effects only

Import raw string#

@2022-01-10
Out of expectation, const fs=require('fs') works.
These won't work

Why folder-level index.js#

@2022-01-11
It's just for importing and exporting easier. The name is confusing, we can make it asset/asset.ts too. The problem is not the index.ts es. Rather a bad pattern on using them. We shouldn’t write any code in index.ts, instead only export and import, and maybe some typing definition.
origin

Async iterator to array#

@2022-01-13
From How can I convert an async iterator to an array?

async function toArray(asyncIterator) {
  const arr = [];
  for await (const i of asyncIterator) arr.push(i);
  return arr;
}