Why is property declared in a constructor of a class not exist?

Issue

constructor (service: MyService) {}

ngOnInit() {
    this.service.init();
}

In the above code, I'm getting:-

Property `service` does not exist on type 'MyComponment'

Yet, if I declare service as private it works. What is going on here?

--

[Angular 8.2.12, TypeScript 3.5.3]

Solution

From the docs:

Parameter properties are declared by prefixing a constructor parameter with an accessibility modifier or readonly, or both. Using private for a parameter property declares and initializes a private member; likewise, the same is done for public, protected, and readonly.

Without the prefix, the constructor parameter is nothing more than a method parameter, and you would have to manually assign it to a declared class property from the constructor itself.

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Answered By - jitender