substring() returns a portion of a string and it’s similar to slice(), with some key differences.
If any parameter is negative, it is converted to 0.
If any parameter is higher than the string length, it is converted to the length of the string.
So:
'This is my car'.substring(5) //'is my car'
'This is my car'.substring(5, 10) //'is my'
'This is my car'.substring(5, 200) //'is my car'
'This is my car'.substring(-6) //'This is my car'
'This is my car'.substring(-6, 2) //'Th'
'This is my car'.substring(-6, 200) //'This is my car'