A brief analysis of the methods of substring and substr in js_javascript skills

1. substring method: is used to extract the characters between two specified subscripts in the string substring(start,end)

Start and end positions, zero-based index

Parameter Description
start Required. A nonnegative integer that specifies the position in stringObject of the first character of the substring to be extracted.
stop is optional. A nonnegative integer that is one position in the stringObject that is one more than the last character of the substring to be extracted. If this parameter is omitted, the returned substring will go to the end of the string.

Return value

A new string value containing a substring of stringObject whose content is all characters from start to stop-1, and whose length is stop minus start.

Description

The substring returned by the

substring method includes the characters at start but not the characters at end.
If start and end are equal, then this method returns an empty string (that is, a string of length 0).
If start is greater than end, the method swaps the two parameters before extracting the substring.
If start or end is negative, it is replaced by 0.

2. substr method

Definition and usage

The

substr method is used to return a substring of the specified length starting from the specified position.

Grammar

stringObject.substr(start [, length ])

Parameter Description
start Required. The starting position of the desired substring. The first character in the string has index 0.
length is optional. The number of characters that should be included in the returned substring.

Description

If start is a negative number, then start=str.length start.
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 stringObject.

Small example:

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));--------------"56789"
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));------------"9"
alert(str.substr(-1,-5));-----------""  

The above is a brief introduction to the methods of substring and substr in js. I hope it will be helpful to everyone's learning.