调用构造函数时出现“错误TS2554：预期有1个参数，但有0。”

Question

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();

Answer 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();