| // Copyright (c) 2013 The Chromium Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style license that can be |
| // found in the LICENSE file. |
| |
| /** |
| * @fileoverview Assertion support. |
| */ |
| |
| /** |
| * Verify |condition| is truthy and return |condition| if so. |
| * @template T |
| * @param {T} condition A condition to check for truthiness. Note that this |
| * may be used to test whether a value is defined or not, and we don't want |
| * to force a cast to Boolean. |
| * @param {string=} opt_message A message to show on failure. |
| * @return {T} A non-null |condition|. |
| */ |
| function assert(condition, opt_message) { |
| if (!condition) { |
| let message = 'Assertion failed'; |
| if (opt_message) { |
| message = message + ': ' + opt_message; |
| } |
| const error = new Error(message); |
| const global = function() { |
| /** @type {boolean} */ |
| this.traceAssertionsForTesting; |
| return this; |
| }(); |
| if (global.traceAssertionsForTesting) { |
| console.warn(error.stack); |
| } |
| throw error; |
| } |
| return condition; |
| } |
| |
| /** |
| * Call this from places in the code that should never be reached. |
| * |
| * For example, handling all the values of enum with a switch() like this: |
| * |
| * function getValueFromEnum(enum) { |
| * switch (enum) { |
| * case ENUM_FIRST_OF_TWO: |
| * return first |
| * case ENUM_LAST_OF_TWO: |
| * return last; |
| * } |
| * assertNotReached(); |
| * return document; |
| * } |
| * |
| * This code should only be hit in the case of serious programmer error or |
| * unexpected input. |
| * |
| * @param {string=} opt_message A message to show when this is hit. |
| */ |
| function assertNotReached(opt_message) { |
| assert(false, opt_message || 'Unreachable code hit'); |
| } |
| |
| /** |
| * @param {*} value The value to check. |
| * @param {function(new: T, ...)} type A user-defined constructor. |
| * @param {string=} opt_message A message to show when this is hit. |
| * @return {T} |
| * @template T |
| */ |
| function assertInstanceof(value, type, opt_message) { |
| // We don't use assert immediately here so that we avoid constructing an error |
| // message if we don't have to. |
| if (!(value instanceof type)) { |
| assertNotReached( |
| opt_message || |
| 'Value ' + value + ' is not a[n] ' + (type.name || typeof type)); |
| } |
| return value; |
| } |