In-depth understanding of substr and substring_javascript techniques in JS

substr method

Returns a substring of the specified length starting at the specified position.
stringvar.substr(start [, length ])
Parameters
stringvar
Required. The string literal or String object from which the substring is to be extracted.
start
Required. The starting position of the desired substring. The first character in the string has index 0.
length
Optional. The number of characters that should be included in the returned substring.
Description
If length is 0 or negative, an empty string is returned. If this parameter is not specified, the substring will be continued to the end of stringvar.

Example
The following example demonstrates the use of the substr method.

function SubstrDemo(){  
var s, ss; // 声明变量。  
var s = "The rain in Spain falls mainly in the plain.";  
ss = s.substr(12, 5); // 获取子字符串。  
return(ss); // 返回 "Spain"。 
}  

举例：  
<script type="text/javascript">  
var str = "0123456789";//  
alert(str.substring(0));//------------"0123456789"  
alert(str.substring(5));//------------"56789"  
alert(str.substring(10));//-----------""  
alert(str.substring(12));//-----------""  
alert(str.substring(-5));//-----------"0123456789"  
alert(str.substring(-10));//----------"0123456789"  
alert(str.substring(-12));//----------"0123456789"  
alert(str.substring(0,5));//----------"01234"  
alert(str.substring(0,10));//---------"0123456789"  
alert(str.substring(0,12));//---------"0123456789"  
alert(str.substring(2,0));//----------"01"  
alert(str.substring(2,2));//----------""  
alert(str.substring(2,5));//----------"234"  
alert(str.substring(2,12));//---------"23456789"  
alert(str.substring(2,-2));//---------"01"  
alert(str.substring(-1,5));//---------"01234"  
alert(str.substring(-1,-5));//--------""  
alert(str.substr(0));//---------------"0123456789"  
alert(str.substr(5));//---------------"56789"  
alert(str.substr(10));//--------------""  
alert(str.substr(12));//--------------""  
alert(str.substr(-5));//--------------"0123456789"  
alert(str.substr(-10));//-------------"0123456789"  
alert(str.substr(-12));//-------------"0123456789"  
alert(str.substr(0,5));//-------------"01234"  
alert(str.substr(0,10));//------------"0123456789"  
alert(str.substr(0,12));//------------"0123456789"  
alert(str.substr(2,0));//-------------""  
alert(str.substr(2,2));//-------------"23"  
alert(str.substr(2,5));//-------------"23456"  
alert(str.substr(2,12));//------------"23456789"  
alert(str.substr(2,-2));//------------""  
alert(str.substr(-1,5));//------------"01234"  
alert(str.substr(-1,-5));//-----------""  
</script> 

substring method

Returns the substring located at the specified position in the String object.
strVariable.substring(start, end)
"String Literal".substring(start, end)
Parameters
start
Specifies the starting position of the substring, the index starts from 0.
end
Indicates the end position of the substring, indexed starting from 0.
Description
The substring method will return a string containing the substring from start to the end (excluding end ).
The substring method uses the smaller of start and end as the starting point of the substring. For example, strvar.substring(0, 3) and strvar.substring(3, 0) will return the same substring.
If start or end is NaN or negative, replace it with 0.
The length of the substring is equal to the absolute value of the difference between start and end. For example, in strvar.substring(0, 3) and strvar.substring(3, 0) the length of the substring returned is 3.

Example
The following example demonstrates the use of the substring method.

function SubstringDemo(){  
var ss; // 声明变量。  
var s = "The rain in Spain falls mainly in the plain..";  
ss = s.substring(12, 17); // 取子字符串。  
return(ss); // 返回子字符串"Spain"。 
} 

The above article on in-depth understanding of substr and substring in JS is all the content shared by the editor. I hope it can give you a reference, and I hope you will support Script Home.