Type guarding is supported with instanceof and as

Rule arkts-no-is

Severity: error

ArkTS does not support the is operator, which must be replaced by the instanceof operator. Note that the fields of an object must be cast to the appropriate type with the as operator before use.

TypeScript

    class Foo {
        foo: number = 0
        common: string = ""
    }

    class Bar {
        bar: number = 0
        common: string = ""
    }

    function isFoo(arg: any): arg is Foo {
        return arg.foo !== undefined
    }

    function doStuff(arg: Foo | Bar) {
        if (isFoo(arg)) {
            console.log(arg.foo)    // OK
            console.log(arg.bar)    // Compile-time error
        } else {
            console.log(arg.foo)    // Compile-time error
            console.log(arg.bar)    // OK
        }
    }

    doStuff({ foo: 123, common: '123' })
    doStuff({ bar: 123, common: '123' })

ArkTS

    class Foo {
        foo: number = 0
        common: string = ""
    }

    class Bar {
        bar: number = 0
        common: string = ""
    }

    function isFoo(arg: Object): boolean {
        return arg instanceof Foo
    }

    function doStuff(arg: Object): void {
        if (isFoo(arg)) {
            let fooArg = arg as Foo
            console.log(fooArg.foo)     // OK
            console.log(arg.bar)        // Compile-time error
        } else {
            let barArg = arg as Bar
            console.log(arg.foo)        // Compile-time error
            console.log(barArg.bar)     // OK
        }
    }

    function main(): void {
        doStuff(new Foo())
        doStuff(new Bar())
    }