1/* 2 * Copyright (c) 2024 Huawei Device Co., Ltd. 3 * Licensed under the Apache License, Version 2.0 (the "License"); 4 * you may not use this file except in compliance with the License. 5 * You may obtain a copy of the License at 6 * 7 * http://www.apache.org/licenses/LICENSE-2.0 8 * 9 * Unless required by applicable law or agreed to in writing, software 10 * distributed under the License is distributed on an "AS IS" BASIS, 11 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12 * See the License for the specific language governing permissions and 13 * limitations under the License. 14 */ 15 16class Foo { 17 foo: number = 0 18 common: string = "" 19} 20 21class Bar { 22 bar: number = 0 23 common: string = "" 24} 25 26function isFoo(arg: any): arg is Foo { 27 return arg.foo !== undefined 28} 29 30function doStuff(arg: Foo | Bar) { 31 if (isFoo(arg)) { 32 console.log(arg.foo) // OK 33 console.log(arg.bar) // Compile-time error 34 } else { 35 console.log(arg.foo) // Compile-time error 36 console.log(arg.bar) // OK 37 } 38} 39 40doStuff({ foo: 123, common: '123' }) 41doStuff({ bar: 123, common: '123' }) 42 43 44function isFoo2(arg: Object): boolean { 45 return arg instanceof Foo 46} 47 48function doStuff2(arg: Object): void { 49 if (isFoo2(arg)) { 50 let fooArg = arg as Foo 51 console.log(fooArg.foo) // OK 52 console.log(arg.bar) // Compile-time error 53 } else { 54 let barArg = arg as Bar 55 console.log(arg.foo) // Compile-time error 56 console.log(barArg.bar) // OK 57 } 58} 59 60function main(): void { 61 doStuff2(new Foo()) 62 doStuff2(new Bar()) 63}