tailscale/client/web/src/utils/util.ts

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause

/**
 * assertNever ensures a branch of code can never be reached,
 * resulting in a Typescript error if it can.
 */
export function assertNever(a: never): never {
  return a
}

/**
 * noop is an empty function for use as a default value.
 */
export function noop() {}

/**
 * isObject checks if a value is an object.
 */
export function isObject(val: unknown): val is object {
  return Boolean(val && typeof val === "object" && val.constructor === Object)
}

/**
 * pluralize is a very simple function that returns either
 * the singular or plural form of a string based on the given
 * quantity.
 *
 * TODO: Ideally this would use a localized pluralization.
 */
export function pluralize(signular: string, plural: string, qty: number) {
  return qty === 1 ? signular : plural
}

/**
 * isTailscaleIPv6 returns true when the ip matches
 * Tailnet's IPv6 format.
 */
export function isTailscaleIPv6(ip: string): boolean {
  return ip.startsWith("fd7a:115c:a1e0")
}

/**
 * isPromise returns whether the current value is a promise.
 */
export function isPromise<T = unknown>(val: unknown): val is Promise<T> {
  if (!val) {
    return false
  }
  return typeof val === "object" && "then" in val
}

/**
 * isHTTPS reports whether the current page is loaded over HTTPS.
 */
export function isHTTPS() {
  return window.location.protocol === "https:"
}