Category: JavaScript Answers

Sometimes, we want to convert Moment.js date to users local time zone with JavaScript.

In this article, we’ll look at how to convert Moment.js date to users local time zone with JavaScript.

How to convert Moment.js date to users local time zone with JavaScript?

To convert Moment.js date to users local time zone with JavaScript, we can use the local method.

For instance, we write

const testDateUtc = moment.utc("2022-01-30 10:00:00");
const localDate = moment(testDateUtc).local();

to create a moment UTC datetime object with moment.utc.

Then we call moment with testDateUtc to create a new moment object.

Finally, we call local on it to return testDateUtc converted to the local time zone.

Conclusion

To convert Moment.js date to users local time zone with JavaScript, we can use the local method.

Sometimes, we want to change the behavior of a mocked import with Jest and JavaScript.

In this article, we’ll look at how to change the behavior of a mocked import with Jest and JavaScript.

How to change the behavior of a mocked import with Jest and JavaScript?

To change the behavior of a mocked import with Jest and JavaScript, we call the jest.mock method.

For instance, we write

import { methodToMock } from "the-package-to-mock";

jest.mock("the-package-to-mock", () => ({
  methodToMock: jest.fn(),
}));

it("test1", () => {
  methodToMock.mockImplementation(() => "someValue");
});

it("test2", () => {
  methodToMock.mockImplementation(() => "anotherValue");
});

to call jest.mock to mock the methodToMock method in the the-package-to-mock module.

We set methodToMock to the mock function returned by jest.fn.

Then in our tests, we call methodToMock.mockImplementation with a callback mocks the behavior of methodToMock.

Conclusion

To change the behavior of a mocked import with Jest and JavaScript, we call the jest.mock method.

Sometimes, we want to convert numbers between different bases in JavaScript.

In this article, we’ll look at how to convert numbers between different bases in JavaScript.

How to convert numbers between different bases in JavaScript?

To convert numbers between different bases in JavaScript, we can use the parseInt function.

For instance, we write

const n = parseInt(string, radix)

to call parseInt to convert the number string into the base specified by the radix.

Conclusion

To convert numbers between different bases in JavaScript, we can use the parseInt function.

Sometimes, we want to reset the navigation stack for the home screen with React Navigation and React Native.

In this article, we’ll look at how to reset the navigation stack for the home screen with React Navigation and React Native.

How to reset the navigation stack for the home screen with React Navigation and React Native?

To reset the navigation stack for the home screen with React Navigation and React Native, we can use the navigation.dispatch and the CommonActions.reset methods.

For instance, we write

import { CommonActions } from "@react-navigation/native";

navigation.dispatch(
  CommonActions.reset({
    index: 1,
    routes: [
      { name: "Home" },
      {
        name: "Profile",
        params: { user: "jane" },
      },
    ],
  })
);

to call navigation.dispatch with the object returned by the CommonActions.reset method.

We call CommonActions.reset with an object that resets the navigation state of the app to the have the Home and Profile routes.

The existing navigation state is replaced with the items we called CommonActions.reset with.

Conclusion

To reset the navigation stack for the home screen with React Navigation and React Native, we can use the navigation.dispatch and the CommonActions.reset methods.

Sometimes, we want to override methods with JavaScript.

In this article, we’ll look at how to override methods with JavaScript.

How to override methods with JavaScript?

To override methods with JavaScript, we can use the class syntax.

For instance, we write

class A {
  speak() {
    console.log("I'm A");
  }
}

class B extends A {
  speak() {
    super.speak();
    console.log("I'm B");
  }
}

const a = new A();
a.speak();

const b = new B();
b.speak();

to create class B that inherits from class A.

In it, we override class A‘s speak method by calling super.speak.

Then we add our own behavior for the speak method exclusive to B.

Therefore, when we call a.speak, we get "I'm A".

And when we call b.speak, we get "I'm B".