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jS数组+数组方法重构
2022-07-06 09:15:00 【进阶日记】
javaScript数组和数组方法重构
1. 数组创建
1. 字面量方法
var arr = ['1','2']
2. 函数构造方法
var arr = new Array('a','b')
2. 数组访问
数组变量名加 [索引]
var arr = ['1','2'];
console.log(arr[0])
3. 数组API方法
toString()在默认情况下都会以逗号分隔字符串的形式返回数组项
join()使用指定的字符串用来分隔数组字符串
var arr = [1,5,2,8,10,{ a:1}]; console.log(arr);//[ 1, 5, 2, 8, 10, { a: 1 } ] console.log(arr.toString());//”1,5,2,8,10,[object Object]” console.log(arr.join(""));//”152810[object Object]”
Array.isArray() 用来判断某个变量是否是一个数组对象
Array.from()从类数组对象或者可迭代对象中创建一个新的数组实例
Array.of() 根据一组参数来创建新的数组实例,支持任意的参数数量和类型
var arr = Array.from("abc"); Array.isArray(arr)//true console.log(arr); //输出结果为["a","b","c"] Array.of(1, 2, 3); // [1, 2, 3]
Array.prototype.push() 向数组的末尾添加一个或多个元素,并返回新的长度
Array.prototype.pop()用于删除数组的最后一个元素并返回删除的元素
Array.prototype.shift()用于把数组的第一个元素从其中删除,并返回第一个元素的值
Array.prototype.unshift()向数组的开头添加一个或更多元素,并返回新的长度
//函数分开运行的结果 var arr = ['zs','ls','ww']; // push() 在末尾添加元素 arr.push('123');//['zs','ls','ww','123'] // pop() 删除最后一个元素,返回删除元素 arr.pop();//['zs','ls'] // shift 删除第一个元素,返回删除元素 arr.shift();//['ls','ww']; // unshift 在第一个添加元素 arr.unshift('23')//['23','zs','ls','ww'];
Array.prototype.reverse()用于颠倒数组中元素的顺序
var arr = ['zs','ls','ww']; arr.reverse()//['ww','ls','zs']
Array.prototype.sort()对数组元素进行排序,不传参默认升序
//降序 var arr = [40,100,1,5,25,10]; arr.sort(function(a,b){ return b-a });
Array.prototype.concat()用于连接两个或多个数组
array1.concat(array2,array3,...,arrayX)
Array.prototype.slice()从已有的数组中返回选定的元素
//slice(start,end) var arr = ["a", "b", "c", "d", "e"]; var result = arr.slice(1,3);//b,c
Array.prototype.splice()用于添加或删除数组中的元素
//参数一为从何开始 参数二为删除的元素个数 参数三开始为添加的元素 var arr = ["a", "b", "c", "d"]; arr.splice(2,0,"e","f");//a,b,e,f
Array.prototype.indexOf()返回数组中某个指定的元素位置
var arr = ["Banana", "Orange", "Apple", "Mango"]; var a = arr.indexOf("Apple",0);//从0号位开始查找 返回2
Array.prototype.lastIndexOf()返回一个指定的元素在数组中最后出现的位置,从后向前查
var arr = ["Banana", "Orange", "Apple", "Mango"]; var a = arr.lastIndexOf("Apple",0);//从0号位开始查找 返回2
Array.prototype.every()检测数组所有元素是否都符合指定条件
var ages = [32, 33, 16, 40]; var result = ages.every(function (age) { return age >= 18 }) console.log(result);//输出结果为:false
Array.prototype.some()检测数组中的元素是否满足指定条件
var ages = [32, 33, 16, 40]; var result = ages.some(function (age) { return age >= 18 }) console.log(result);//输出结果为:true
Array.prototype.filter()创建一个新的数组,新数组中的元素是通过检查指定数组中符合条件的所有元素
var ages = [32, 33, 16, 40]; var result = ages.filter(function (age) { return age >= 18 }) console.log(result);//输出结果为:[ 32, 33, 40 ]
Array.prototype.map()返回一个新数组,数组中的元素为原始数组元素调用函数处理后的值
var numbers = [4, 9, 16, 25]; var result = numbers.map(function (number) { return Math.sqrt(number) }) console.log(result);//输出结果为:[ 2, 3, 4, 5 ]
Array.prototype.forEach()调用数组的每个元素,并将元素传递给回调函数
var age = [35,21,32,51]; age.forEach(function (item,index) { console.log(item,index); }) //35 0 //21 1 //32 2 //51 3
4. 数组方法重构
push方法重构
var arr = new Array(); arr = ['123', '24', '214', 124]; //两个方式 // Array.prototype.myPush = function (str) { // if (str == null) { // return this.length; // } else { // this[this.length] = str; // } // return this.length; // } Array.prototype.myPush = function (str) { for (let i = 0; i < arguments.length; i++) { this[this.length] = arguments[i]; } return this.length; } // arr.myPush('12'); // console.log(arr);
pop方法重写
Array.prototype.myPop = function () { if (this.length==0) { return undefined; } let temp = this[this.length - 1] this.length--; return temp; } // arr.myPop() // console.log(arr.myPop());
shift方法重写
Array.prototype.myShift = function () { let temp = this[0]; for (let i = 0; i < this.length; i++) { this[i] = this[i + 1]; } this.length = this.length - 1 return temp; } // arr.myShift() // console.log(arr);
unshift方法重写
var aa = [123, 124, 125] Array.prototype.myUnShift = function () { var result = this.length + arguments.length; for (let i = result; i > 0; i--) { if (i > arguments.length) { this[i - 1] = this[i - 1 - arguments.length] } else { this[i - 1] = arguments[i - 1] } } return result; } // aa.myUnShift('13','666','wrw',123) // console.log(aa);
reverse方法重写
Array.prototype.myReverse = function () { var arr = []; for (let j = 0; j < this.length; j++) { arr[j] = this[j]; } for (let i = 0; i < this.length; i++) { this[i] = arr[this.length - i - 1]; } return this; }
concat方法重写
Array.prototype.myConcat = function (str) { let arr = []; for (let o = 0; o < this.length; o++) { arr[o] = this[o] } if (str == '') { return arr; } for (let x = 0; x < arguments.length; x++) { if (Array.isArray(arguments[x])) { for (let i = 0; i < arguments[x].length; i++) { arr[arr.length] = arguments[x][i] } } else if (!Array.isArray(arguments[x])) { arr[arr.length] = arguments[x] } } return arr; } var q = [123, 53, 1] var x = abc.myConcat('c', q, 'd', q) // console.log(x,abc);
slice方法重写
Array.prototype.mySlice = function (start, end) { let arr = []; if (start > end && end != '') { return this; } else { if (start < 0) { start = this.length + start; } if (end < 0) { end = this.length + end; } if (end == null) { console.log(123); for (let i = start; i < this.length; i++) { arr[i - start] = this[i]; } } else { if (end > this.length) { end = this.length; } for (let j = start; j < end; j++) { arr[j - start] = this[j]; } } } return arr; } // console.log(abc.mySlice(2,4));
forEach重构
Array.prototype.myForEach=function(fun) { for (let i = 0; i < arr.length; i++) { fun(this[i],i,this) } }
every方法重写 方法中的this指向global不指向调用数组 第二个参数修改this指向
Array.prototype.myEvery = function (fun,obj) { for (let i = 0; i < this.length; i++) { if(!(obj?fun.bind(obj)(this[i]):fun(this[i]))){ return false; } } return true; }
some方法重构
Array.prototype.mySome = function (fun,obj) { for (let i = 0; i < this.length; i++) { if((obj?fun.bind(obj)(this[i]):fun(this[i]))){ return true; } } return false; } var result = qq.mySome(function(item) { return item<0 })
map方法重构
Array.prototype.myMap = function(fun,obj) { let arr = []; for (let i = 0; i < this.length; i++) { arr.push(obj?fun.bind(obj)(this[i]):fun(this[i])) } return arr; }
filter方法重构
Array.prototype.myFilter = function(fun,obj) { var result = []; for (let i = 0; i < this.length; i++) { if (obj?fun.bind(obj)(this[i]):fun(this[i])) { result.push(this[i]) } } }
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