The JavaScript string.slice() method

Q: What is the difference between slice() and substring()?

Both extract part of a string, but slice() supports negative indices (counting from the end), while substring() treats negatives as 0 and swaps the arguments if start > end. slice() is the more predictable choice.

Q: How do I get the last few characters of a string?

Use a negative start: str.slice(-3) returns the last three characters.

Q: Should I use substr()?

No — substr() is deprecated. Use slice() (or substring()) in new code.

Method JavaScript All modern browsers Updated June 23, 2026

Quick answer

The slice() method pulls out part of a string and returns it as a new string, from a start index up to (but not including) an end index. "JavaScript".slice(0, 4) gives "Java". It accepts negative indices that count from the end, which is what makes it the most convenient of the substring methods.

Overview

slice() extracts a chunk of a string. Give it a start index and an end index and you get back the characters in between — start included, end excluded. So slice(0, 4) returns the first four characters. Leave off the end and it runs to the finish; leave off both and you get a copy of the whole string.

Its best feature is negative indices: slice(-3) returns the last three characters, and slice(-4, -1) works from the end too. That makes common jobs — grabbing a file extension, trimming the last character — neat one-liners. Strings are immutable, so you always get a new string and the original is untouched.

There are three overlapping methods here, and the confusion is real. slice() handles negatives (use this one). substring() is similar but treats negatives as 0 and swaps its arguments if they're out of order. substr() takes a start and a length and is deprecated. For new code, reach for slice() and you'll rarely need the others.

Syntax

const part = str.slice(start)
const part = str.slice(start, end)

"JavaScript".slice(0, 4)  // "Java"
"JavaScript".slice(-6)    // "Script"

Parameters

The string.slice() method accepts the following parameters.

Parameter	Description
`start`	Index to start from (0-based). Negative counts from the end of the string.
`end`	Optional. Index to stop before (not included). Negative counts from the end. Defaults to the string length.

Example

Live example

<pre id="out" style="font:15px ui-monospace,monospace"></pre>
<script>
  const file = 'report-2026.pdf';

  const ext  = file.slice(-3);          // last 3 chars
  const name = file.slice(0, file.indexOf('.'));

  document.getElementById('out').textContent =
    'name: ' + name + '\n' +
    'ext:  ' + ext; // name: report-2026 / ext: pdf
</script>

Best practices

Prefer slice() over substring() and the deprecated substr() — it handles negative indices.
Use negative indices for "from the end" jobs, like str.slice(-4) for a file extension.
Remember end is exclusive: slice(0, 3) returns three characters.
Use the return value — strings are immutable, so the original never changes.

Frequently asked questions

What is the difference between slice() and substring()?

Both extract part of a string, but slice() supports negative indices (counting from the end), while substring() treats negatives as 0 and swaps the arguments if start > end. slice() is the more predictable choice.

How do I get the last few characters of a string?

Use a negative start: str.slice(-3) returns the last three characters.

Does slice() change the original string?

No. Strings are immutable, so it returns a new string and leaves the original as it was.

Should I use substr()?

No — substr() is deprecated. Use slice() (or substring()) in new code.

string.replaceAll() string.split()

References