16.javascript 数组的操作
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1.通过索引号即下标访问数字元素
var cars = ["Saab", "Volvo", "BMW"]; cars[0]; //结果是:Saab
2.修改数组中的值,索引方式修改
var cars = ["Saab", "Volvo", "BMW"]; cars[0] = "Opel"; //结果:cars = ["Opel", "Volvo", "BMW"];
3.直接输出完整数组
var cars = ["Audi", "BMW", "porsche"]; document.getElementById("demo").innerHTML = cars; //结果:Audi,BMW,porsche
4.获取数组长度Array.length;
var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits.length; // fruits 的长度是 4
5.访问数组最后一个数组元素
fruits = ["Banana", "Orange", "Apple", "Mango"]; var last = fruits[fruits.length - 1];
6.遍历数组两种方法
第一种方法for循环
var fruits, text, fLen, i; fruits = ["Banana", "Orange", "Apple", "Mango"]; fLen = fruits.length; text = "<ul>"; for (i = 0; i < fLen; i++) text += "<li>" + fruits[i] + "</li>";
第二种方法Array.forEach()
var fruits, text; fruits = ["Banana", "Orange", "Apple", "Mango"]; text = "<ul>"; fruits.forEach(myFunction); text += "</ul>"; document.getElementById("demo").innerHTML = text; function myFunction(value) text += "<li>" + value + "</li>";
7.向数组结尾添加新元素Array.push();,方法返回新数组的长度
var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits.push("Lemon"); // 向 fruits 添加一个新元素 (Lemon) //结果:fruits = ["Banana", "Orange", "Apple", "Mango", "Lemon"];
8.空数组中,通过下标方式可添加数组元素
var person = []; person[0] = "Bill"; person[1] = "Gates"; person[2] = 62; var x = person.length; // person.length 返回 3 var y = person[0]; // person[0] 返回 "Bill" //结果:person=["Bill", "Gates", 62];
9.如何判断一个变量是不是数组:Array.isnArray();
var fruits = ["Banana", "Orange", "Apple", "Mango"]; Array.isArray(fruits); // 返回 true
自己创建isArray()函数判断
function isArray(x) return x.constructor.toString().indexOf("Array") > -1;
假如对象由给定的构造器创建,则 instanceof 运算符返回 true:
var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits instanceof Array // 返回 true
10.数组转字符串Array.toString();
var fruits = ["Banana", "Orange", "Apple", "Mango"]; document.getElementById("demo").innerHTML = fruits.toString(); //结果:Banana,Orange,Apple,Mango
11.将所有的数组元素结合成为一个字符串Array.join(),可对元素与元素直接使用自定义连接符
var fruits = ["Banana", "Orange","Apple", "Mango"]; document.getElementById("demo").innerHTML = fruits.join(" * "); //结果:Banana * Orange * Apple * Mango
12.删除数组中最后一个元素Array.pop();,返回值是被删除的那个元素
var fruits = ["Banana", "Orange", "Apple", "Mango"]; var x = fruits.pop(); // 从 fruits 删除最后一个元素("Mango"),x的值是"Mango"
13.删除数组中首个也就是第一个元素Array.shift();,返回值是被删除的那个元素
var fruits = ["Banana", "Orange", "Apple", "Mango"]; var x = fruits.shift(); // 从 fruits 删除第一个元素 "Banana",x的值是"Banana"
14.向数组开头添加新元素Array.unshift();,返回值是新数组的长度
var fruits = ["Banana", "Orange", "Apple", "Mango"]; var x = fruits.unshift("Lemon"); // x值是 5
15.使用delete运算符删除数组中的元素,不建议用,会使数组留下未定义的空洞
var fruits = ["Banana", "Orange", "Apple", "Mango"]; delete fruits[0]; // 把 fruits 中的首个元素改为 undefined
16.splice()方法可自定义需要添加的元素,也可删除元素
添加元素:
var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits.splice(2, 0, "Lemon", "Kiwi");
第一个2表示开始位置
第二个0表示需要删除多少个元素
第三,第四表示需要插入的元素,可省略
删除元素
var fruits = ["Banana", "Orange", "Apple", "Mango"]; fruits.splice(0, 1); // 删除 fruits 中的第一个元素
17.将A,B两个数组合并,甚至更多的数组合并,合并成一个新的数组A.concat(B,C,D)
var myGirls = ["Cecilie", "Lone"]; var myBoys = ["Emil", "Tobias", "Linus"]; var myChildren = myGirls.concat(myBoys); // 连接 myGirls 和 myBoys
var arr1 = ["Cecilie", "Lone"]; var arr2 = ["Emil", "Tobias", "Linus"]; var arr3 = ["Robin", "Morgan"]; var myChildren = arr1.concat(arr2, arr3); // 将arr1、arr2 与 arr3 连接在一起
var arr1 = ["Cecilie", "Lone"]; var myChildren = arr1.concat(["Emil", "Tobias", "Linus"]);
18.使用slice()裁剪數組,返回裁剪后的新数组
一個參數時(參數為數字),表示從几下标位置开始裁剪,直接裁剪到最后一个数组元素,
//从索引1的位置开始裁剪,一直到结尾 var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"]; var citrus = fruits.slice(1); document.getElementById("demo").innerHTML = fruits + "<br><br>" + citrus; //结果:Orange,Lemon,Apple,Mango
两个参数时,表示从索引几开始裁剪,裁剪到索引几(不包括)
var fruits = ["Banana", "Orange", "Lemon", "Apple", "Mango"]; var citrus = fruits.slice(1,3); document.getElementById("demo").innerHTML = fruits + "<br><br>" + citrus; //结果:Orange,Lemon
19.数组转换成字符串Array.toString();
var fruits = ["Banana", "Orange", "Apple", "Mango"]; document.getElementById("demo").innerHTML = fruits.toString(); //结果:Banana,Orange,Apple,Mango
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错误代码:错误域 = NSCocoaErrorDomain 代码 = 3840“JSON 文本没有以数组或对象和允许未设置片段的选项开头。”