// document.querySelector[All]
// element.querySelector[All]

// VD 1

const array = document.querySelectorAll('div.vidu div.phantucon')
for (const element of array) {
  console.log(element.textContent)
}

const array = document.querySelectorAll('div.vidu')
for (const container of array) {
  const subset = container.querySelectorAll('div.phantucon')
  for (const element of subset) {
    console.log(element.textContent)
  }
}

// VD 2
// SQL: FROM output SELECT x * x

const output = input.map(x => x * x)

const output = []
for (const x of input) output.push(x * x)

// VD 3
// SQL: FROM output SELECT x WHERE x > 3

const output = input.filter(x => x > 3)

const output = []
for (const x of input) if (x > 3) output.push(x)

// VD 4

const output = input.map(callback)

const output = []
for (const x of input) output.push(callback(x))

function callback () {}

// VD 5

const output = input.reduce((sum, x) => sum + x, 0)

let output = 0
for (const x of input) output = output + x

// VD 6

const output = input.sort((a, b) => a < b)

const output = Array.from(input)
for (let i = 0; i != output.length - 1; ++i) {
  const a = input[i]
  const b = input[i + 1]
  if (a < b) {
    output[i + 1] = a
    output[i] = b
  }
}

// VD 7

const output = input.reduce(callback, initial)

let output = initial
for (const x of input) output = callback(output, x)

// VD 8

array.sort(callback)
// if callback(a, b) returns -1, -2, -3, ..., +∞ >>> a is placed before b
// if callback(a, b) returns +1, +2, +3, ..., -∞ >>> b is placed before a
// if callback(a, b) returns 0 >>> a and b are treated equal

// VD 9 Chữ hoa, chữ thường

'abcDEFghiJKL'.toUpperCase() // => 'ABCDEFGHIJKL'
'abcDEFghiJKL'.toLowerCase() // => 'abcdefghijkl'