正文

• 全局对象
  • node 中的 全局 this指向的是module.exports，而不是全局对象global
    • 在外部函数中的this指向global，匿名函数也是
  • 浏览器环境下全局this就是window
    • 在外部函数中的this指向window，匿名函数也是

• reverse
  - 不改变原数组版，如果想要改变，那么不要deepClone即可

javascript">Array.prototype.myReverse = function () {
    const length = this.length
    const arr = deepClone(this)
    for (let i = 0; i < Math.floor(length / 2); i++) {
        let temp = arr[i]
        arr[i] = arr[length - 1 - i]
        arr[length - 1 - i] = temp
    }
    return arr
}

const arr = ['a', 'b', 'c', 'd']

console.log(arr.myReverse());
console.log(arr)

function deepClone(target) {
    if (typeof target !== 'object') {
        return target
    }

    let result
    if ({}.toString.call(target) === '[object Object]') {
        result = {}
    } else {
        result = []
    }

    for (let key in target) {
        if (target.hasOwnProperty(key)) {
            result[key] = deepClone(target[key])
        }
    }

    return result
}

• forEach
  • 兼容node环境或者浏览器环境

javascript">Array.prototype.myForEach = function (callback, thisArg = typeof global === 'undefined' ? window : global) {
   for (let i = 0; i < this.length; i++) {
       callback.call(thisArg, this[i], i, this)
   }
}

• filter
  • 兼容node环境或者浏览器环境
  • 改变原数组

javascript">Array.prototype.myFilter = function (callback, thisArg = typeof global === 'undefined' ? window : global) {
        for (let i = 0; i < this.length; i++) {
            if (!callback.call(thisArg, this[i], i, this)) {
                this.splice(i, 1)
                i--
            }
        }
    }

• map
  • 兼容node环境或者浏览器环境
  • 改变原数组

javascript">Array.prototype.myMap = function (callback, thisArg = typeof global === 'undefined' ? window : global) {
        for (let i = 0; i < this.length; i++) {
            this[i] = callback.call(thisArg, this[i], i, this)
        }
    }

• every
  • some同理，省略
  • 兼容node环境或者浏览器环境

javascript">Array.prototype.myEvery = function (callback, thisArg = typeof global === 'undefined' ? window : global) {
   let flag = true

   for (let i = 0; i < this.length; i++) {
       if (!callback.call(thisArg, this[i], i, this)) {
           flag = false
           break
       }
   }

   return flag
}

• find
  • findIndex同理，省略
  • 兼容node环境或者浏览器环境

javascript">Array.prototype.myFind = function (callback, thisArg = typeof window === "undefined" ? global : window) {
    for (let i = 0; i < this.length; i++) {
        if (callback.call(thisArg, this[i], i, this)) {
            return this[i]
        }
    }
}

• 字符串是否是回文序列（不区分大小写）

javascript">String.prototype.isPalindrome = function () {
    for (let i = 0; i < Math.floor(this.length / 2); i++) {
        if (this[i].toLowerCase() !== this[this.length - 1 - i].toLowerCase()) {
            return false
        }
    }
    return true
}

String.prototype.isPalindrome = function () {
    return this.toLowerCase() === this.toLowerCase().split('').reverse().join('')
}

结语

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