String,math common functions in JS

String object:
1.length Properties
Description: Gets the length of the string
Instance:
var str= "abc";
var i=str.length;//output:3



2.charAt () method
Description: Finds a character in a specified index (position) from a string
Instance:
var str= "abc";
var str1=str.charat (2);//output:c
String index starting from 0



3.indexOf () method
Description: Gets the position (subscript) where the substring first appears in the parent string, and outputs "1" if it is not found;
Format: Index (sub-string, starting index);
Instance:
var str= "abcdb";
var i=str.indexof (' B ');//output:1
var j=str.indexof (' B ', 2);//output:4



4.lastIndexOf () method
Description: Gets the position where the substring first appears in the parent string, unlike IndexOf, where LastIndexOf starts the search from the last character.
Enter "-1" if not found
Instance:
var str= "ABCDCBD";
Alert (Str.lastindexof (' BD '));//output:5
Alert (Str.lastindexof (' B ', 3));//output:1, here the second parameter is 3 for the end of index 3, so the output is 1.
Alert (Str.lastindexof (' B ', 5));//output:5, here the second parameter is 5 for the end of index 5, so the output is 5.
Note: LastIndexOf is a search starting from the last character, then you specify: Str.lastindexof (' B ', 5) It will search for the index of ' B ' forward from the position of index 5



4.substring () method
Description: A partial string that intercepts a female string.
Format: substring (starting index, terminating index)
Instance:
var str= "ABCDEFG";
Alert (str.substring (0,3));//output:abc
Alert (str.substring (3,0));
The output:abc,substring () function automatically determines which is the starting point and that is the termination.
So the parameter 0 is put to the front, the parameter 3 is put in the back, so the output is: ABC
Alert (str.substring (3));//OUTPUT:DEFG

Note: The return value does not contain the character of the sleepover Index, but until the previous character.



5.replace () method
Description: The substring specified in the replacement string is the corresponding string
Format: replace ("Specified substring", "Replace with corresponding string")
Instance:
var str= "ABCDBFGBC";
Alert (str.replace ("BC", ' KK '));//OUTPUT:AKKDBFGBC
Note: Replace only the first string that matches
This is different from C #, see the following example:
String tt = "ABCDCD";
Console.WriteLine (TT. Replace ("CD", "AA"));
Output: Abaaaa,c# 's Replac function searches the string for all "CD" Strings and replaces the "CD" String with "AA".

Math function

1. Max function syntax

Math.max (A, b,..., x, y);

Max function Parameters: A, b,..., x, y--numbers of type number, can be decimals, integers, positive, negative, 0.

2. Max function return value
Returns the larger value in a number of values

3. Math Other related functions:
Math.random ()
Returns a random number between 0 and 1.

4, Math.Round ()
Rounds rounding.

5, Math.ceil ()
Return value: Returns the integer that is greater than or equal to x and closest to.
Note: If x is a positive number, the decimal is "in" and if X is a negative number, the decimal is "placed".

6, Math.floor ()
Return value: Returns the integer that is less than or equal to x and closest to.
Note: If x is a positive number, the decimal is "in" and if X is a negative number, the decimal is "in".

String,math common functions in JS