ES6（五）数组扩展

数组

// 空数组
let arr = Array.of()
log(arr)
// 数组
let arr1 = Array.of(1, 2, 3, 4, 5, 6, 7)
log(arr1)

转义成数组

let p = document.querySelectorAll('p')
let pArr = Array.from(p)
pArr.forEach(item => {
  log(item.textContent)
})

遍历数组操作

// [2, 6, 10]
log(Array.from([1, 3, 5], (item) => {
  return item * 2
}))

填充

// [7, 7, 7]
log([1, '2', undefined].fill(7))
// ["a", 7, 7]  从1位置开始，一直到第3个
log(['a', 'b', 'c'].fill(7, 1, 3))

取index和值

let arr = ['1', 'c', '3']
// 0 1 2
for (let index of arr.keys()) {
  log(index)
}
// 1 c 3
for (let value of arr.values()) {
  log(value)
}
// index对应value
for (let [index, value] of arr.entries()) {
  log(index + ' ' + value)
}

数组替换

let arr = ['q', 'w', 'e', 'r', 't']
// ["r", "w", "e", "r", "t"]
// 起始位置0，要替换的值从第3个位置读取，结束位置是4
console.log(arr.copyWithin(0, 3, 4))

查找位置

let arr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
// 返回7的位置  6
console.log(arr.indexOf(7))
// 只找查询到的第一个值  4
console.log(arr.find(item => {
  return item > 3
}))
// 返回查询到的第一个值的index
console.log(arr.findIndex(item => {
  return item > 3
}))
// 6
console.log(arr.findIndex(item => {
  return item === 7
}))
// true
console.log(arr.includes(1))
// true
console.log([1, 2, NaN].includes(NaN))

reduce

      let arr = [0, 1, 2, 3, 4].reduce(function (accumulator, currentValue, currentIndex, array) {
        // accumulator 累计器
        // currentValue 当前值
        // currentIndex 当前索引
        // array 数组
        return accumulator + currentValue
      })
      console.log(arr)

 拼接数组

let arr = ['tom', 'jerry'];
let arr2 = [1, 2];

let newArr = arr.concat(arr2);
console.log(newArr);

let arr = ['tom', 'jerry'];
let arr2 = [1, 2];

arr.push.apply(arr, arr2);
console.log(arr)

let arr = ['tom', 'jerry'];
let arr2 = [1, 2];

arr.push(...arr2);
console.log(arr)