What is substring()?
substring() method returns part of the string from start index upto end index but excluding the endindex. It extracts characters between two indices from a string and return the substring. It does not change the original string.
Syntax:
substring(indexStart)
substring(indexStart, indexEnd)
Parameters:
indexStart – Index of first character to include in substring.
indexEnd – It is optional. It denotes the first character to exclude from the returned string.
When indexEnd is not there, the substring() method returns characters upto the end of the string.
Return value – A new sub string containing part of original string.
What will happen if both index start and end are same?
const str = ‘Abaython’
str.substring(3,3)
When both start and end index are same will return an empty string.
If start index greater than end index?
const str = ‘Abaython’
str.substring(4,2)Output:
ay
Here it will simply swap the parameters as,
str.substring(2,4)
So, the output is ay.
If indexEnd is omitted?
const str = ‘Abaython’
str.substring(4)
Output:
thon
Here it will return upto the end of the string starting from index 4
Substring() vs slice()
Though in both methods the parameters are same, the main difference is using negative values.
In substring() method negative values are considered as zero.
const s = 'Abaython';
console.log(s.substring(-4,5))
Output:
Abayt
Here -4 is considered as 0 and returns from the start of the string.
Keypoints to note:
Similarities:
- In both methods the parameters are same. If start and end index are equal both returns an empty string.
- If end index is omitted then the characters are extracted upto the end of the string.
- Any parameter greater than string length then string length is used instead.
- NaN treated as 0.
Differences:
- In case of startindex > endindex,
Substring() method swaps the parameters.
Slice() method returns empty string
- If any argument has negative values,
Substring() method treats them as 0
Slice() method counts from the end of the string for negative values