javascript substring v.s. slice

What is the difference between String.slice and String.substring?

stackoverflow.com › questions › 2243824 › what-is-the-difference-between-string-slice-and-string-substring

slice() works like substring() with a few different behaviors.

Syntax: string.slice(start, stop);
Syntax: string.substring(start, stop);

What they have in common:

If start equals stop: returns an empty string
If stop is omitted: extracts characters to the end of the string
If either argument is greater than the string's length, the string's length will be used instead.

Distinctions of substring():

If start > stop, then substring will swap those 2 arguments.
If either argument is negative or is NaN, it is treated as if it were 0.

Distinctions of slice():

If start > stop, slice() will return the empty string. ("")
If start is negative: sets char from the end of string, exactly like substr().
If stop is negative: sets stop to: string.length – Math.abs(stop) (original value), except bounded at 0 (thus, Math.max(0, string.length + stop)) as covered in the ECMA specification.

Source: Rudimentary Art of Programming & Development: Javascript: substr() v.s. substring()

Answer from Daniel Vassallo on Stack Overflow

Stack Overflow

stackoverflow.com › questions › 2243824 › what-is-the-difference-between-string-slice-and-string-substring

javascript - What is the difference between String.slice and String.substring? - Stack Overflow

TL;DR:

If you know the index (the position) on which you'll stop (but NOT include), use slice().
If you know the length of characters to be extracted, you could use substr(), but that is discouraged as it is deprecated.

Otherwise, read on for a full comparison

Syntax

string.slice(start,end)
string.substr(start,length)
string.substring(start,end)

Note #1: slice()==substring()

What it does?

slice() extracts parts of a string and returns the extracted parts in a new string.
substr() extracts parts of a string, beginning at the character at the specified position, and returns the specified number of characters.
substring() extracts parts of a string and returns the extracted parts in a new string.

Note #2: slice()==substring()

Changes the Original String?

slice() doesn't
substr() doesn't
substring() doesn't

Note #3: slice()==substr()==substring()

Using Negative Numbers as an Argument

slice() selects characters starting from the end of the string
substr() selects characters starting from the end of the string
substring() doesn't perform

Note #4: slice()==substr()

If the First Argument is Greater than the Second

slice() doesn't perform
substr() since the Second Argument is NOT a position, but length value, it will perform as usual, with no problems
substring() will swap the two arguments, and perform as usual

The First Argument

slice() required; starting Index
substr() required; starting Index
substring() required; starting Index

Note #5: slice()==substr()==substring()

The Second Argument

slice() optional; the position (up to, but not including) where to end the extraction
substr() optional; the number of characters to extract
substring() optional; the position (up to, but not including) where to end the extraction

Note #6: slice()==substring()

What if the Second Argument is Omitted?

slice() selects all characters from the start-position to the end of the string
substr() selects all characters from the start-position to the end of the string
substring() selects all characters from the start-position to the end of the string

Note #7: slice()==substr()==substring()

So, you can say that there's a difference between slice() and substr(), while substring() is basically a copy of slice().

If you want substr's functionality:

"foobarbaz".substr(index, length);

without using a deprecated feature, you can just do:

"foobarbaz".substring(index, length + index);

And get the exact same results bar all of the edge-cases, like negative index/length.

Mastering JS

masteringjs.io › tutorials › fundamentals › substring-vs-slice

JavaScript `substring()` vs `slice()` - Mastering JS

A big difference with substring() is that if the 1st argument is greater than the 2nd argument, substring() will swap them. slice() returns an empty string if the 1st argument is greater than the 2nd argument.

Videos