function cast () {
return Array.prototype.slice.call(arguments);
}
cast('a','b','c','d'); // ["a", "b", "c", "d"]

function cast () {
return [].slice.call(arguments);
}
cast('a','b','c','d'); // ["a", "b", "c", "d"]

let arrayLike = {
'0': 'a',
'1': 'b',
'2': 'c',
length: 3
}
console.log(Array.from(arrayLike)); // ["a","b","c"]

function cast (){
return [...arguments]
}
cast('a','b','c'); // ["a","b","c"]

let arr = Array.from('w3cplus.com')
console.log(arr); // ["w","3","c","p","l","u","s",".","c","o","m"]
let namesSet = new Set(['a', 'b'])
let arr2 = Array.from(namesSet) 
console.log(arr2); //["a","b"]

let arr = Array.from([1, 2, 3]);
console.log(arr); // [1,2,3]

Array.from(arrayLike, x => x * x);
// 等同于
Array.from(arrayLike).map(x => x * x);
Array.from([1, 2, 3], (x) => x * x)
// [1, 4, 9]

Array.from({ length: 2 }, () => 'jack')
// ['jack', 'jack']

function countSymbols(string) {
return Array.from(string).length;
}

function typesOf () {
return Array.from(arguments, value => typeof value)
}
typesOf(null, [], NaN)
// <- ['object', 'object', 'number']

function typesOf (...all) {
return all.map(value => typeof value)
}
typesOf(null, [], NaN)
// <- ['object', 'object', 'number']
Array.of

Array.of = function of () {
return Array.prototype.slice.call(arguments)
}

Array.prototype.slice.call([1, 2, 3])
// <- [1, 2, 3]
Array.of(1, 2, 3)
// <- [1, 2, 3]
Array.of(3)
// <- [1]

new Array()
// <- []
new Array(undefined)
// <- [undefined]
new Array(1)
// <- [undefined x 1]
new Array(3)
// <- [undefined x 3]
new Array(1, 2)
// <- [1, 2]
new Array(-1)
// <- RangeError: Invalid array length

Array.of()
// <- []
Array.of(undefined)
// <- [undefined]
Array.of(1)
// <- [1]
Array.of(3)
// <- [3]
Array.of(1, 2)
// <- [1, 2]
Array.of(-1)
// <- [-1]

function ArrayOf(){
return [].slice.call(arguments);
}

Array.prototype.copyWithin(target, start = 0, end = this.length)

var items = [1, 2, 3, ,,,,,,,]; // <- [1, 2, 3, undefined x 7]

items.copyWithin(6, 1, 3)
// <- [1, 2, 3, undefined × 3, 2, 3, undefined × 2]

// 将3号位复制到0号位
[1, 2, 3, 4, 5].copyWithin(0, 3, 4)
// [4, 2, 3, 4, 5]
// -2相当于3号位，-1相当于4号位
[1, 2, 3, 4, 5].copyWithin(0, -2, -1)
// [4, 2, 3, 4, 5]
// 将3号位复制到0号位
[].copyWithin.call({length: 5, 3: 1}, 0, 3)
// {0: 1, 3: 1, length: 5}
// 将2号位到数组结束，复制到0号位
var i32a = new Int32Array([1, 2, 3, 4, 5]);
i32a.copyWithin(0, 2);
// Int32Array [3, 4, 5, 4, 5]
// 对于没有部署TypedArray的copyWithin方法的平台
// 需要采用下面的写法
[].copyWithin.call(new Int32Array([1, 2, 3, 4, 5]), 0, 3, 4);
// Int32Array [4, 2, 3, 4, 5]
Array.prototype.fill

['a', 'b', 'c'].fill(0)
// <- [0, 0, 0]
new Array(3).fill(0)
// <- [0, 0, 0]

['a', 'b', 'c',,,].fill(0, 2)
// <- ['a', 'b', 0, 0, 0]
new Array(5).fill(0, 0, 3)
// <- [0, 0, 0, undefined x 2]

new Array(3).fill({})
// <- [{}, {}, {}]

new Array(3).fill(function foo () {})
// <- [function foo () {}, function foo () {}, function foo () {}]
Array.prototype.find

[1, 2, 3, 4, 5].find(item => item > 2)
// <- 3
[1, 2, 3, 4, 5].find((item, i) => i === 3)
// <- 4
[1, 2, 3, 4, 5].find(item => item === Infinity)
// <- undefined

[1, 5, 10, 15].find(function(value, index, arr) {
return value > 9;
}) // 10
Array.prototype.findIndex

[1, 2, 3, 4, 5].find(item => item > 2)
// <- 2
[1, 2, 3, 4, 5].find((item, i) => i === 3)
// <- 3
[1, 2, 3, 4, 5].find(item => item === Infinity)
// <- -1

[NaN].indexOf(NaN)
// -1
[NaN].findIndex(y => Object.is(NaN, y))
// 0

for (let index of ['a', 'b'].keys()) {
console.log(index);
}
// 0
// 1
for (let elem of ['a', 'b'].values()) {
console.log(elem);
}
// 'a'
// 'b'
for (let [index, elem] of ['a', 'b'].entries()) {
console.log(index, elem);
}
// 0 "a"
// 1 "b"

let letter = ['a', 'b', 'c'];
let entries = letter.entries();
console.log(entries.next().value); // [0, 'a']
console.log(entries.next().value); // [1, 'b']
console.log(entries.next().value); // [2, 'c']