JavaScript 数组方法汇总

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自用笔记：本文属于自用笔记，不做详解，仅供参考。
在此记录自己已理解并开始遵循的前端代码规范。What How Why

创建数组

隐式创建

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var arr=['Audi', 'BMW', 'Volvo']

直接实例化

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var arr=new Array('Audi', 'BMW', 'Volvo')

快速构建数组

直接构建法:

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let arr = ['mock', 'mock', 'mock']

循环法: for循环

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let arr = []
for(var i = 0;i < 3;i++){
  arr.push('mock')
}

快速填充数组

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let newArr = new Array(3).fill('mock');

构建顺序(倒序数组)

快速填充数组

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let newArr = new Array(10).fill(1).map((item, index) => index + 1)
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let funss = (m, n) => Array.apply(null, new Array(m)).map(() => n++)

数组最大值

es6拓展运算符…

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
Math.max(...arr)

es5 apply(与方法1原理相同)

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
Math.max.apply(null,arr)

for循环

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
let max = arr[0]
for (let i = 0; i < arr.length - 1; i++) {
  max = arr[i] < arr[i+1] ? arr[i+1] : arr[i]
}

数组sort()

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
arr.sort((num1, num2) => {
  return num1 - num2 < 0
})
arr[0]

数组reduce

array.reduce(function(total, currentValue, currentIndex, arr), initialValue)

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
arr.reduce((num1, num2) => {
  return num1 > num2 ? num1 : num2}
)

数组去重

ES6的set

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var arr = [-1, 1, 101, -52, 10, 1001, 1001]
console.log(Array.from(new Set(arr)))

var arr = [-1, 1, 101, -52, 10, 1001, 1001]
console.log([...new Set(arr)])

过滤push

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```
Array.prototype.distinct = function () {
  var arr = this, result = [], len = arr.length
  for (i = 0; i < len; i++) {
    for (j = i + 1; j < len; j++) {
      if (arr[i] === arr[j]) {
        j = ++i
      }
    }
    result.push(arr[i])
  }
  return result
}
var arra = [1, 2, 3, 4, 4, 1, 1, 2, 1, 1, 1]
arra.distinct()
// [3, 4, 2, 1]

## 过滤splice
优点：简单易懂
缺点：占用内存高，速度慢

``` javascript
Array.prototype.distinct = function () {
  var arr = this, len = arr.length
  for (i = 0; i < len; i++) {
    for (j = i + 1; j < len; j++) {
      if (arr[i] === arr[j]) {
        arr.splice(j, 1)
        len--
        j--
      }
    }
  }
  return arr
}
var arra = [1, 2, 3, 4, 4, 1, 1, 2, 1, 1, 1]
arra.distinct()
// [1, 2, 3, 4]

利用对象过滤

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Array.prototype.distinct = function () {
  var arr = this, obj = {}, result = [], len = arr.length
  for (i = 0; i < len; i++) {
    if (!obj[arr[i]]) {
      obj[arr[i]] = true;
      result.push(arr[i])
    }
  }
  return result
}
var arra = [1, 2, 3, 4, 4, 1, 1, 2, 1, 1, 1]
arra.distinct()
// [1, 2, 3, 4]

数组递归去重

运用递归的思想，先排序，然后从最后开始比较，遇到相同，则删除

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Array.prototype.distinct = function () {
  var arr = this, len = arr.length
  arr.sort(function(a, b) {
    return a - b
  })
  function loop(index) {
    if (index >= 1) {
      if (arr[index] === arr[index - 1]) {
        arr.splice(index, 1)
      }
      loop(index - 1)
    }
  }
  loop(len - 1)
  return arr
}
var arra = [1, 2, 3, 4, 4, 1, 1, 2, 1, 1, 1]
arra.distinct()

利用indexOf以及forEach

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Array.prototype.distinct = function () {
  var arr = this, result = [], len = arr.length
  arr.forEach(function (v, i, arr) {
    if (arr.indexOf(v, i+1) === -1) {
      result.push(v)
    }
  })
  return result
}
var arra = [1, 2, 3, 4, 4, 1, 1, 2, 1, 1, 1]
arra.distinct()

数组合并去重

concat()方法

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var a = [1, 2, 3];
var b = [4, 5, 2];
function concatArray(a, b) {
	a = a.concat(b)
	a = a.distinct()
	return a
}
concatArray(a, b)
// [1, 3, 4, 5, 2]

apply()方法

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var a = [1, 2, 3];
var b = [4, 5, 2];
function concatArray(a, b) {
	Array.prototype.push.apply(a, b)
	a = a.distinct()
	return a
}
concatArray(a, b)
// [1, 3, 4, 5, 2]