Detailed explanation of the use of indexof in JavaScript

I believe many friends will be confused when they see the title. What is indexof? That's right, many friends who have never been exposed to JavaScript don't know much about indexof, and even friends who know JavaScript may not understand it. So today we will take you through a detailed explanation of the use of indexof in JavaScript. !

String.IndexOf 方法 (Char, [startIndex], [count])

Reports the index of the first occurrence of the specified character in this instance. The search starts at the specified character position and checks the specified number of character positions.
Parameters
value
The Unicode character to look for. The search for value is case-sensitive.

startIndex（Int32）

Optional, search starting position. If not set, it starts from 0.

count（Int32）

Optional, the number of character positions to check.
Return value
If the character is found, it is the index position of value; otherwise, it is -1 if it is not found.
IndexOf()
Find the position where the specified character or string first appears in the string, and return the first index value, such as:

str1.IndexOf("字")； //查找“字”在str1中的索引值（位置）
str1.IndexOf("字串")；//查找“字串”的第一个字符在str1中的索引值（位置）
str1.IndexOf("字",start,end)；//从str1第start+1个字符起，查找end个字符，查找“字”在字符串STR1中的位置[从第一个字符算起]注意:start+end不能大于str1的长度

The indexof parameter is string , looks for the first occurrence of the parameter string in the string and returns that position. For example, string s="0123dfdfdf"; int i=s.indexof("df"); then i==4.

If you need a more powerful string parsing function, you should use the Regex class and use regular expressions to match strings.

indexof(): Position characters and strings from front to back in the string; all return values ​​refer to the absolute position in the string, if empty, it is - 1

string test="asdfjsdfjgkfasdsfsgfhgjgfjgdddd";
test.indexof('d') =2 //从前向后 定位 d 第一次出现的位置
test.indexof('d',1) =2 //从前向后 定位 d 从第三个字符串第一次出现的位置
test.indexof('d',5,2) =6 //从前向后 定位 d 从第5 位开始查，查2位，即 从第5位到第7位；
lastindexof() ：在字符串中从后向前定位字符和字符串；、

The usage is exactly the same as indexof().

The following introduces IndexOfAny ||lastindexofany

They accept character array as a variable. Other methods are the same as above, returning the earliest character in the array. The subscript positions that appear

are as follows

char[] bbv={'s','c','b'};
string abc = "acsdfgdfgchacscdsad";
Response.Write(abc.IndexOfAny(bbv))=1
Response.Write(abc.IndexOfAny(bbv, 5))=9
Response.Write(abc.IndexOfAny(bbv, 5, 3))=9
lastindexofany 同上。

Summary:

By pairing I believe that after studying this article, many friends who don’t understand indexof will have a certain understanding. Next time you see indexof, you will know what it does. I hope it will be helpful to you!

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