ui/webui/resources/js/assert.js

   1 // Copyright (c) 2013 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 /**
   6  * @fileoverview Assertion support.
   7  */
   8
   9 /**
  10  * Verify |condition| is truthy and return |condition| if so.
  11  * @template T
  12  * @param {T} condition A condition to check for truthiness.  Note that this
  13  *     may be used to test whether a value is defined or not, and we don't want
  14  *     to force a cast to Boolean.
  15  * @param {string=} opt_message A message to show on failure.
  16  * @return {T} A non-null |condition|.
  17  */
  18 function assert(condition, opt_message) {
  19   'use strict';
  20   if (!condition) {
  21     var msg = 'Assertion failed';
  22     if (opt_message)
  23       msg = msg + ': ' + opt_message;
  24     throw new Error(msg);
  25   }
  26   return condition;
  27 }
  28
  29 /**
  30  * Call this from places in the code that should never be reached.
  31  *
  32  * For example, handling all the values of enum with a switch() like this:
  33  *
  34  *   function getValueFromEnum(enum) {
  35  *     switch (enum) {
  36  *       case ENUM_FIRST_OF_TWO:
  37  *         return first
  38  *       case ENUM_LAST_OF_TWO:
  39  *         return last;
  40  *     }
  41  *     assertNotReached();
  42  *     return document;
  43  *   }
  44  *
  45  * This code should only be hit in the case of serious programmer error or
  46  * unexpected input.
  47  *
  48  * @param {string=} opt_message A message to show when this is hit.
  49  */
  50 function assertNotReached(opt_message) {
  51   throw new Error(opt_message || 'Unreachable code hit');
  52 }
  53
  54 /**
  55  * @param {*} value The value to check.
  56  * @param {function(new: T, ...)} type A user-defined constructor.
  57  * @param {string=} opt_message A message to show when this is hit.
  58  * @return {T}
  59  * @template T
  60  */
  61 function assertInstanceof(value, type, opt_message) {
  62   if (!(value instanceof type)) {
  63     throw new Error(opt_message ||
  64                     value + ' is not a[n] ' + (type.name || typeof type));
  65   }
  66   return value;
  67 }