JavaScript indexOf () method and LastIndexOf () method

One, definition and usage

The IndexOf () method returns the position of the first occurrence of a specified string value in a string.

The LastIndexOf () method returns the location of the last occurrence of a specified string value, which is searched from behind at the specified position in a string.

Grammar

Stringobject.indexof (Searchvalue,fromindex)

Stringobject.lastindexof (Searchvalue,fromindex)

IndexOf () method

Parameters	Description
Searchvalue	Necessary. Specifies the string value that needs to be retrieved.
Fromindex	An optional integer parameter. Specifies where to start retrieving in the string. Its legal value is 0 to stringobject.length-1. If this argument is omitted, it is retrieved from the first character of the string.

LastIndexOf () method

Parameters	Description
Searchvalue	Necessary. Specifies the string value that needs to be retrieved.
Fromindex	An optional integer parameter. Specifies where to start retrieving in the string. Its legal value is 0 to stringobject. length-1. If this argument is omitted, the search begins at the last character of the string.

return value

LastIndexOf () method if Searchvalueexists before the fromindex position in Stringobject , the last one that appears is returned the location of the Searchvalue.

Description

The IndexOf () method retrieves the string stringobject from beginning to end to see if it contains substring searchvalue. The location at which to begin retrieving is at the fromindex of the string or at the beginning of the string (when no fromindex is specified). If a searchvalue is found, the position of the first occurrence of the Searchvalue is returned. The character position in Stringobject is starting at 0.

The LastIndexOf () method retrieves the string stringobjectfrom the end of the head to see if it contains a substring searchvalue. The location at which to begin retrieving is at the fromindex of the string or at the end of the string (when no fromindex is specified). If a searchvalueis found, the position of the first character of the Searchvalue in stringobject is returned. The character position in Stringobject is starting at 0.

Second, hints and notes

Note: Both the IndexOf () method and the LastIndexOf () method are case-sensitive!

If the string value that you want to retrieve does not appear, the method returns-1.

Example 1:

The effect is as follows:
Example 2:
The effect is as follows:
(I do not know if the reader will have doubts, why the results are the same?) In this long-winded, because the LastIndexOf () method is a backward search, but the return position is from the beginning of the number and calculation, so the result is as above. ）
Download: http://www.cnblogs.com/iceflorence/p/5825286.html
2017-08-26 11:08:00
JavaScript indexOf () method and LastIndexOf () method