String.prototype.slice()

slice(start[, end])

slice() extracts a portion of a string and returns it as a new string. The original string remains unchanged. This method is useful when you need to extract substrings based on positions, whether counting from the start or from the end using negative indices.

Syntax

slice(start)
slice(start, end)

Parameters

Parameter	Type	Default	Description
start	number	—	Index where extraction begins. Negative indices count from the end of the string.
end	number	string.length	Index where extraction ends (exclusive). Negative indices count from the end.

Examples

Extracting from the start

const greeting = "Hello, World!";

// Extract first 5 characters
console.log(greeting.slice(0, 5));
// Hello

// Omitting end extracts to the end of the string
console.log(greeting.slice(7));
// World!

Using negative indices

const text = "Hello, World!";

// Extract last 6 characters
console.log(text.slice(-6));
// World!

// Extract middle portion using negative end index
console.log(text.slice(0, -1));
// Hello, World

When start exceeds length

const str = "Hello";

// If start is greater than or equal to string length, returns empty
console.log(str.slice(10));
// (empty string)

console.log(str.slice(5));
// (empty string)

Start greater than end

const str = "Hello";

// When start is greater than end, slice() returns empty string
console.log(str.slice(5, 0));
// (empty string)

Common Patterns

Extract file extension from filename

const filename = "report.pdf";
const ext = filename.slice(filename.lastIndexOf("."));
console.log(ext);
// .pdf

Get last N characters

const id = "user-12345";
const suffix = id.slice(-5);
console.log(suffix);
// 12345

Truncate text with ellipsis

const longText = "This is a very long description that needs truncating";
const maxLength = 20;

const truncated = longText.length > maxLength
  ? longText.slice(0, maxLength) + "..."
  : longText;

console.log(truncated);
// This is a very long...

Remove surrounding quotes or brackets

const quoted = "\"Hello World\"";
const unquoted = quoted.slice(1, -1);
console.log(unquoted);
// Hello World

Extract domain from URL

const url = "https://api.example.com/v1/users";
const domain = url.slice(8, url.indexOf("/", 8));
console.log(domain);
// api.example.com

When to Use

Use slice() when you need to:

• Extract substrings with precise control over start and end positions
• Work with negative indices to count from the end
• Maintain consistency with Arrayslice() behavior

When Not to Use

Avoid slice() when:

• You need case-insensitive matching — use a regex or toLowerCase() first
• You’re searching for a substring by content — use indexOf() or includes() instead
• You need the argument-swap behavior that substring() provides

See Also

• string::split — Split string into array
• string::substring — Similar method with different index handling