Substring and substr methods in JavaScript (JS)

1. substring Method

Definition and usage

The substring method is used to extract characters of a string between two specified subscripts.

Syntax

Stringobject. substring (start, stop)

Parameter description
Start is required. A non-negative integer that specifies the position of the first character of the substring to be extracted in the stringobject.
Optional. A non-negative integer is 1 more than the position of the last character of the substring to be extracted in the stringobject. If this parameter is omitted, the returned substring ends at the end of the string.

Return Value

A new string. The value of this string contains a substring of stringobject. Its content is all characters from start to stop-1, and its length is stop minus start.

Description

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

2. substr Method

Definition and usage

The substr method returns a substring of the specified length starting from the specified position.

Syntax

Stringobject. substr (start [, length])

Parameter description
Start is required. The starting position of the required substring. The index of the first character in the string is 0.
Length is optional. The number of characters to be included in the returned substring.

Description

If the length is 0 or negative, an empty string is returned.
If this parameter is not specified, the substring will continue to the end of the stringobject.

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 (01234); ---------- ""
alert (Str. substring (0123456789); --------- ""
alert (Str. substring (0123456789); --------- ""
alert (Str. substring (2, 0); ---------- "01"
alert (Str. substring (2, 2); ---------- ""
alert (Str. substring (234); ---------- ""
alert (Str. substring (23456789); --------- ""
alert (Str. substring (2,-2); --------- "01"
alert (Str. substring (-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 (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 ));-----------""

References:

Http://www.w3school.com.cn/js/jsref_substring.asp

Http://www.w3school.com.cn/js/jsref_substr.asp