الرموز المعروفة جيدًا

console.log(typeof Symbol.iterator)
console.log(typeof Symbol.toPrimitive)

const arr = [10, 20]
const it = arr[Symbol.iterator]()
console.log(it.next().value)

const range = {
  from: 1,
  to: 3,
  [Symbol.iterator]() {
    let cur = this.from
    const last = this.to
    return {
      next() {
        return cur <= last ? { value: cur++, done: false } : { value: undefined, done: true }
      }
    }
  }
}
for (const n of range) {
  console.log(n)
}

const nums = {
  [Symbol.iterator]() {
    let i = 0
    return { next() { return i < 3 ? { value: i++, done: false } : { value: undefined, done: true } } }
  }
}
console.log([...nums])

const money = {
  amount: 50,
  [Symbol.toPrimitive](hint) {
    if (hint === "number") return this.amount
    return "$" + this.amount
  }
}
console.log(+money)
console.log(money + "")

const obj = {
  [Symbol.toPrimitive](hint) {
    return hint
  }
}
console.log(+obj)
console.log(obj + "")
console.log(String(obj))

const widget = {
  [Symbol.toStringTag]: "Widget"
}
console.log(Object.prototype.toString.call(widget))

class Even {
  static [Symbol.hasInstance](num) {
    return num % 2 === 0
  }
}
console.log(4 instanceof Even)
console.log(3 instanceof Even)

const set = new Set([1, 2, 3])
console.log([...set])

const list = {
  items: ["a", "b"],
  [Symbol.iterator]() {
    return this.items[Symbol.iterator]()
  }
}
for (const x of list) {
  console.log(x)
}

console.log(typeof Symbol.iterator)
console.log(typeof Symbol.toStringTag)
console.log(typeof Symbol.hasInstance)

const r = { [Symbol.iterator]() { let i = 0; return { next() { return i < 2 ? { value: i++, done: false } : { value: 0, done: true } } } } }
console.log([...r])