JavaScript substring() mehtod
The substring()
method in JavaScript is used to extract a portion of a string between two specified indices. This method returns a new string that contains the characters from the original string, starting at the specified startIndex
and ending just before the specified endIndex
.
Syntax:
startIndex
: The index at which to begin extraction (inclusive). If this index is greater than the length of the string, it is treated as equal to the string's length.endIndex
(optional): The index at which to end extraction (exclusive). If omitted,substring()
extracts characters to the end of the string. If this index is greater than the length of the string, it is treated as equal to the string's length.
Return Value:
- Returns a new string that contains the extracted portion of the original string. The original string remains unchanged.
Example 1: Basic Usage
In this example, substring(7, 12)
extracts the characters from index 7
to index 12
, resulting in the substring "World"
.
Example 2: Omitted End Index
If the endIndex
is omitted, substring()
will extract characters from the startIndex
to the end of the string.
Here, substring(7)
extracts the substring starting from index 7
to the end of the string.
Example 3: Handling Indices Out of Range
If startIndex
is greater than endIndex
, substring()
will swap the two indices.
In this case, since startIndex
is 12
and endIndex
is 7
, the method swaps them and effectively behaves like substring(7, 12)
.
Example 4: Negative Indices
If either index is negative, it is treated as 0
. This means that negative indices do not have the same behavior as they do with the slice()
method.
Here, the negative startIndex
is treated as 0
, so the method extracts characters from the beginning of the string.
Example 5: Start Index Greater Than Length
If startIndex
is greater than or equal to the string's length, the method will return an empty string.
In this case, since the startIndex
is 15
, which is greater than the length of the string, the method returns an empty string.
Example 6: Original String Remains Unchanged
The original string is not modified by the substring()
method.
Summary:
- The
substring()
method extracts a portion of a string between two specified indices. - It takes two parameters:
startIndex
(inclusive) andendIndex
(exclusive). - If the
endIndex
is omitted, the method extracts to the end of the string. - If
startIndex
is greater thanendIndex
, the indices are swapped. - Negative indices are treated as
0
, and indices out of range are adjusted accordingly. - The method returns a new string without modifying the original string.