• JavaScript
• data type
• assignment
• array […]
  • access data array1[index1]
  • loop array
  • string
• function
  • anonymous function
  • variadic function
• comparison
• object
  • quick initialization
  • access attribute
  • immutable object Object.freeze(…)
  • method
  • class class Class1{…}
    • constructor constructor(…){…}
    • getter/setter get var1() {…}/set var1(…) {…}

JavaScript

data type

• no char
• undefined
  • nullish coalescing operator ??
    give default value if the expression before is null or undefined
  • optional chaining ?
    skip method chain and return undefined if expression before is undefined

assignment

• fallback || execute if the former one fail

array […]

can contain multiple types of data

access data array1[index1]

• .length
• .push() .pop() work like stack
• .unshift() .shift() work like queue
• .splice(index,number,…) remove number items from index and insert …
• .reduce(fun1) take variable into function and put result back
• spread (deep copy) [...arr1]
• rest [attr1, ...arr2] = arr1

loop array

• the C way
• for… of loop
• .forEach(callback)

string

is just immutable array

formatted string

`blah ${var1}…`

• .toUpperCase()
• .toLowerCase()
• .trim()
• .slice(start,end)
  • a.slice(1) return substring excluding a[0]
  • a.slice(-1) return a[a.length - 1]

function

function fun1(var1,…) {
    // …
}

anonymous function

(var1,…) => {
    // …
}

minimum var1 => expression1

variadic function

• arguments magic variable: array-like object
• rest parameter (arg0, …, ...args): array

comparison

• strong comparison === !== does not convert type
• weak comparison == != convert type

object

{
    attr1: lit1,
    // …
}

rather dictionary

• delete attribute
• .hasOwnProperty(attr) check if has attr
• rest {attr1, ...obj2} = obj1
• spread obj2 = {...obj1, attr1: val1}

quick initialization

{
    attr1,
    attr2,
    // …
}

is equivalent to

{
    attr1: attr1,
    attr2: attr2,
    // …
}

access attribute

• .attr1
• object1[attr1]

immutable object Object.freeze(…)

method

defined inside of the object block

class class Class1{…}

constructor constructor(…){…}

use constructor new

getter/setter get var1() {…}/set var1(…) {…}