The difference between JS interception string substr and substring methods_javascript skills

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 will be 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.

Copy code The code is as follows:

function SubstrDemo(){
var s, ss ; // Declare variables.
var s = "The rain in Spain falls mainly in the plain.";
ss = s.substr(12, 5); // Get the substring.
return(ss); // Return "Spain".
}

Example:
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substring method

Returns the substring at the specified position in the String object.
strVariable.substring(start, end)
"String Literal".substring(start, end)
Parameter
start
Indicates the starting position of the substring, the index starts from 0 Start counting.
end
specifies the end position of the substring, the index starts 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.

Copy code

The code is as follows:

function SubstringDemo(){
var ss; / / Declare variables.
var s = "The rain in Spain falls mainly in the plain..";
ss = s.substring(12, 17); // Get the substring.
return(ss); // Return substring.
}

For more basics, please refer to: http://www.jb51.net/w3school/js/jsref_substring.htm
http://www.jb51.net/w3school/js/jsref_substr.htm