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().
  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 from Daniel Vassallo on Stack Overflow
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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
Top answer
1 of 9
1236

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().
  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()

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191

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.

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