Generators in JavaScript

javascript_generator.js

// 1. Use the Default Iterator from an Array
const abcs = ["A", "B", "C"]

const createIterator = abcs[Symbol.iterator].bind(abcs)

const iterator = createIterator()

for (const i of iterator) {
    console.log(i)
}

// 2. Create Your First Iterator in JavaScript
let i = 0

const next = () => ({
    value: i++,
    done: i > 10
})

const iterator = {
    [Symbol.iterator]() {
        return {
            next
        }
    }
}

for (let value of iterator) {
    console.log(value)
}

// 3. Create a Custom Iterator for Any Array
const abcs = ["A", "B", "C"]

const numbers = [1, 2, 3]

const createReverseIterator = array => ({
    [Symbol.iterator]() {
        let i = array.length
        return {
            next: () => ({
                value: array[--i],
                done: i < 0
            })
        }
    }
})


for (let value of createReverseIterator(numbers)) {
    console.log(value)
}

// 4. Create Your First Generator in JavaScript
const abcs = ["A", "B", "C"]

const numbers = [1, 2, 3]

const createReverseIterator = array => ({
    [Symbol.iterator]() {
        let i = array.length
        return {
            next: () => ({
                value: array[--i],
                done: i < 0
            })
        }
    }
})

const reverseIterator = function* (array) {
    let i = array.length
    while (i > 0) {
        yield array[--i]
    }
}


for (let value of reverseIterator(numbers)) {
    console.log(value)
}

// 5. Stop a Generator from Yielding Values
const abcs = ["A", "B", "C"]

const reverseIterator = function* (array) {
    let i = array.length
    while (i > 0) {
        yield array[--i]
    }
}

const iterator = reverseIterator(abcs)

console.log(iterator.next())
console.log(iterator.return())
console.log(iterator.next())
console.log(iterator.next())

// 6. Yield an Array, String, or Any Iterable from a Generator
const abcs = ["A", "B", "C"]

const reverseIterator = function* (array) {
    yield* array
    yield* array.map(letter => letter.toLowerCase())
    yield Math.random()
}

const iterator = reverseIterator(abcs)

for (let value of iterator) {
    console.log(value)
}

// 7. Avoid Nested For Loops with Generators
const abcs = ["A", "B", "C"]

const shoutIterator = function* (word) {
    yield word + "!"
    yield word + "!!"
    yield word + "!!!"
}

const reverseIterator = function* (array) {
    yield* shoutIterator(array[0])
    yield* shoutIterator(array[1])
    yield* shoutIterator(array[2])
}

const iterator = reverseIterator(abcs)

for (let value of iterator) {
    console.log(value)
}

// 8. Understand Each Iteration Inside a Generator
function* generator() {
    //first iteration
    yield 1

    //second iteration
    console.log("second")
    yield 2

    //third iteration
    console.log("third")
}

const iterator = generator()

console.log(iterator.next())
console.log(iterator.next())
console.log(iterator.next())

// 9. Use a Generator Like a Closure
function makeAdder(x) {
    return function (y) {
        return x + y
    }
}

let add2 = makeAdder(2)

function* makeAdderGenerator(x) {
    let y = yield x
    while (true) {
        y = yield x + y
    }
}

let add2Iterator = makeAdderGenerator(2)
console.log(add2Iterator.next())
console.log(add2Iterator.next(1))
console.log(add2Iterator.next(2))

// 10. Create a State Machine with a Generator
function* stateMachine(state) {
    let transition
    while (true) {
        if (transition === "INCREMENT") {
            state++
        }
        if (transition === "DECREMENT") {
            state--
        }
        transition = yield state
    }
}

const iterator = stateMachine(0)

console.log(iterator.next())
console.log(iterator.next("INCREMENT"))
console.log(iterator.next("INCREMENT"))
console.log(iterator.next("DECREMENT"))

// 11. Create a `range` Helper Function with a Generator
function* range(start, end) {
    while (start < end) yield start++
}

for (let value of range(0, 10)) {
    console.log(value)
}

console.log([...range(0, 100)])

// 12. Compare a Generator to Using Array Map and Filter
let names = ["John", "Mindy", "Sally"]

let result = names.filter(name => name.includes("y")).map(name => name.toLocaleLowerCase())
console.log(result)

function* format(array) {
    for (let value of array) {

        if (value.includes("y")) {
            yield value.toLowerCase()
            return
        }
    }
}

console.log([...format(names)])