Getting “error TS2554: Expected 1 arguments, but got 0.” when calling a constructor

问题

Getting an error

error TS2554: Expected 1 arguments, but got 0.

when the class instance is called. How can I fix this?

class ErrorHandler {

    constructor(private errorService: BackendErrorsService) {}
    getError() {
        console.log('error called');
    }
}

const instance = new ErrorHandler().getError();

回答1:

Angular automatically resolve dependencies of components and services. However, when you call your class like that:

const instance = new ErrorHandler().getError();

Then you need to supply a dependency BackendErrorsService. Something like that:

let backendErrorsService = new BackendErrorsService();
const instance = new ErrorHandler(backendErrorsService ).getError();

来源：https://stackoverflow.com/questions/57990675/getting-error-ts2554-expected-1-arguments-but-got-0-when-calling-a-construc