JS数组的查找、截取和拼接
程序员文章站
2023-12-22 22:36:10
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<!DOCTYPE html>
<html lang="en">
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<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>数组的查找、截取和拼接</title>
</head>
<body>
<script>
/*
indexOf(searchValue[,fromIndex])
查找目标字符串中，是否包含searchValue，如果包含，返回第一次出现的索引，如果不包含,返回-1
- searchValue 要查找的值
- fromIndex 查找的起始位置，如果不填，默认为0
如果大于或者等于length，则返回-1
如果说是一个负数（如果这个负数的绝对值超过length，则fromIndex为0），根据倒数来确认查找的位置
length + fromIndex
*/
var arr1 = ["E","a","b","c","a","d"];
console.log(arr1.indexOf("vv")); //打印：-1
console.log(arr1.indexOf("a",arr1.length)); //打印：-1
console.log(arr1.indexOf("a", -2)); //打印：4
console.log(arr1.indexOf("a", -50)); //打印：1
/*
lastIndexOf(searchValue[,fromIndex])
返回数组中指定的值最后一次出现的位置,如果不存在，则返回-1
fromIndex
搜索的起始位置，默认为length
如果大于或者等于length，则为length
如果是一个负数，则倒数找到对应的起始位置
length - fromIndex
如果负数的绝对值大于length,则返回 -1
*/
console.log(arr1.lastIndexOf("a", arr1.length - 3)); //打印：1
console.log(arr1.lastIndexOf("a", 50)); //打印：4
console.log(arr1.lastIndexOf("vv")); //打印：-1
/*
slice(begin,end)
用于截取数组中的内容，返回一个新数组
- begin
- 如果不给，默认为0
- 截取的起始位置
- 如果值超过了length，就会返回一个空数组给你
- 如果是一个负数（负数的绝对值超过了length，就会默认从0开始截取），那就说明从倒数第begin开始截取
length + begin
- end
- 如果不给，默认到数组结尾
- 控制截取的结束位置
- 如果小于（从位置上来说）bengin，会得到一个空字符串
- 如果是负数（如果负数的绝对值超过了length，那么就会得到一个空字符串），那么就说明从倒数第end个结束。
- 如果超过了length，默认也只到数组的结尾位置
begin是包含在内的，end是不包含在截取范围内
*/
var arr2 = ["a","b","c","d","e"];
console.log(arr2.slice(2)); //打印：["c","d","e"]
console.log(arr2); //打印：["a","b","c","d","e"]
console.log(arr2.slice(50)); //打印：[]
console.log(arr2.slice(-2)); //打印：["d","e"]
console.log(arr2.slice(-50)); //打印：["a","b","c","d","e"]
console.log(arr2.slice(2,-1)); //打印：["c","d"]
console.log(arr2.slice(0, -50)); //打印：[]
console.log(arr2.slice(0, 50)); //打印：["a","b","c","d","e"]
/*
深拷贝：
数据拷贝过来后，和原数组之间完全没有任何关系了
浅拷贝：
数据拷贝过来后，里面的第一层的基本类型是没有关联了，但是里面的复杂类型，依旧是有关联
赋址:
数据不管是基本类型，还是复杂类型，都和原来的是相关联的
*/
//赋址
arr3 = arr2
arr3[0] = "123";
console.log(arr2,arr3); //打印：["123","b","c","d","e"] ["123","b","c","d","e"]
var arr4 = ["a","b","c","d","e"];
var arr5 = arr4.slice();
arr5[0] = "123";
console.log(arr4,arr5); //打印：["a","b","c","d","e"] ["123","b","c","d","e"]
var arr6 = [[1,2,3],"a"];
var arr7 = arr6.slice();
arr6[0][0] = "good";
console.log(arr6,arr7); //打印：[["good",2,3],"a"] [["good",2,3],"a"]
/*
concat 用于拼接两个或两个以上的数组，并返回一个新数组，并不会改变原有数组的值
*/
var arr8 = ["I"];
var arr9 = ["love"];
var arr10 = ["you!"];
console.log(arr8.concat(arr9,arr10)); //打印：["I", "love", "you!"]
/*
join（sparator）
把数组拼接起来，以字符串的方式，进行返回，如果不给参数，默认以逗号进行间隔
sparator
决定以什么符号对数组的里面进行拼接
** 如果数组是一个空数组的话，则会返回一个空字符串
*/
var arr11 = ["I", "love", "you!"]
console.log(arr11.join(" ")); //打印：I love you!
var arr12 = [""];
console.log(arr12.join()); //打印：空
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