std/path/windows/is_absolute.ts

// Copyright 2018-2024 the Deno authors. All rights reserved. MIT license.
// This module is browser compatible.

import { CHAR_COLON } from "../_common/constants.ts";
import { assertPath } from "../_common/assert_path.ts";
import { isPathSeparator, isWindowsDeviceRoot } from "./_util.ts";

/**
 * Verifies whether provided path is absolute.
 *
 * @example Usage
 * ```ts
 * import { isAbsolute } from "@std/path/windows/is-absolute";
 * import { assert, assertFalse } from "@std/assert";
 *
 * assert(isAbsolute("C:\\foo\\bar"));
 * assertFalse(isAbsolute("..\\baz"));
 * ```
 *
 * @param path The path to verify.
 * @returns `true` if the path is absolute, `false` otherwise.
 */
export function isAbsolute(path: string): boolean {
  assertPath(path);

  const len = path.length;
  if (len === 0) return false;

  const code = path.charCodeAt(0);
  if (isPathSeparator(code)) {
    return true;
  } else if (isWindowsDeviceRoot(code)) {
    // Possible device root

    if (len > 2 && path.charCodeAt(1) === CHAR_COLON) {
      if (isPathSeparator(path.charCodeAt(2))) return true;
    }
  }
  return false;
}