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 * @return {T} 58 * @template T 59 */ 60 function assertInstanceof(value, type) { 61 if (!(value instanceof type)) 62 throw new Error(value + ' is not a[n] ' + (type.name || typeof type)); 63 return value; 64 } 65
