Syntax

Arrow Function

const test = () => {
       ...
}

equal

const test = function(){
       ...
}

Rest Param & Spread Syntax (...)

Rest Param

• accept the numbers of argument as a array

function myFun(a,  b, ...manyMoreArgs) {
  console.log("a", a)
  console.log("b", b)
  console.log("manyMoreArgs", manyMoreArgs)
}

myFun("one", "two", "three", "four", "five", "six")
// Console Output:
// a, one
// b, two
// manyMoreArgs, ["three", "four", "five", "six"]

Spread Syntax

• Expand array into numbers of argument/ number

• Expand object into numbers of key-value pair

function sum(x, y, z) {
  return x + y + z;
}

const numbers = [1, 2, 3];

console.log(sum(...numbers));
// expected output: 6

let numberStore = [0, 1, 2];
let newNumber = 12;
numberStore = [...numberStore, newNumber];
console.log(numberStore);
// [0, 1, 2, 12]

let obj = {test:1, test2:2};
let objClone = { ...obj , test3:3};
console.log(objClone);
// {test:1, test2:2, test3:3}

function test(...hi) {
  console.log(test);
}
test(1,2,3);
// [1,2,3]

Destructing

const student = { id:1, name:"Tom"};
const {id , name} = student;
console.log(id);
// 1
const array = [1, 2 , 3];
const [num1, , num3] = array;
console.log(num3);
// 3

?? vs ||

• ?? return next item when first item is undefined or null

• || includes 0 , false , empty string checking

console.log(false ?? 1);
console.log("" ?? 1);
console.log(0 ?? 1);
console.log(null ?? 1);
console.log(undefined ?? 1);

// false
// ""
// 0
// null
// undefined

console.log(false || 1);
console.log("" || 1);
console.log(0 || 1);
console.log(null || 1);
console.log(undefined || 1);
// 1
// 1
// 1
// 1
// 1

=== vs ==

console.log(num === obj); // false
console.log(num === str); // false
console.log(obj === str); // false
console.log(1 === true); // false

console.log(num == obj); // true
console.log(num == str); // true
console.log(obj == str); // true
console.log(1 == true); // true

• Better to use ===