Skip to main content
Using Deno in production at your company? Earn free Deno merch.
Give us feedback
Module

std/path/posix/extname.ts

Deno standard library
Go to Latest
File
// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.// This module is browser compatible.
import { CHAR_DOT } from "../_common/constants.ts";import { assertPath } from "../_common/assert_path.ts";import { isPosixPathSeparator } from "./_util.ts";
/** * Return the extension of the `path` with leading period. * @param path with extension * @returns extension (ex. for `file.ts` returns `.ts`) */export function extname(path: string): string { assertPath(path);
let startDot = -1; let startPart = 0; let end = -1; let matchedSlash = true; // Track the state of characters (if any) we see before our first dot and // after any path separator we find let preDotState = 0; for (let i = path.length - 1; i >= 0; --i) { const code = path.charCodeAt(i); if (isPosixPathSeparator(code)) { // If we reached a path separator that was not part of a set of path // separators at the end of the string, stop now if (!matchedSlash) { startPart = i + 1; break; } continue; } if (end === -1) { // We saw the first non-path separator, mark this as the end of our // extension matchedSlash = false; end = i + 1; } if (code === CHAR_DOT) { // If this is our first dot, mark it as the start of our extension if (startDot === -1) startDot = i; else if (preDotState !== 1) preDotState = 1; } else if (startDot !== -1) { // We saw a non-dot and non-path separator before our dot, so we should // have a good chance at having a non-empty extension preDotState = -1; } }
if ( startDot === -1 || end === -1 || // We saw a non-dot character immediately before the dot preDotState === 0 || // The (right-most) trimmed path component is exactly '..' (preDotState === 1 && startDot === end - 1 && startDot === startPart + 1) ) { return ""; } return path.slice(startDot, end);}