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

Question

Does anyone know what the difference is between these two methods?

String.prototype.slice String.prototype.substring 

Answer 1

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

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

What they have in common:

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

Distinctions of substring():

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

Distinctions of slice():

1. If start > stop, slice() will return the empty string. ("")
2. If start is negative: sets char from the end of string, exactly like substr() in Firefox. This behavior is observed in both Firefox and IE.
3. 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 2

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, use substr().

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?

• The slice() method extracts parts of a string and returns the extracted parts in a new string.
• The substr() method extracts parts of a string, beginning at the character at the specified position, and returns the specified number of characters.
• The substring() method 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()==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 #3: 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, indicates: Starting Index
• substr() Required, indicates: Starting Index
• substring() Required, indicates: Starting Index

Note #4: 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 #5: 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 #6: slice()==substr()==substring()

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