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
 * @param path to be verified as absolute
 */
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;
}