Category: JavaScript Answers

Sometimes, we want to get distance between two points in canvas with JavaScript.

In this article, we’ll look at how to get distance between two points in canvas with JavaScript.

How to get distance between two points in canvas with JavaScript?

To get distance between two points in canvas with JavaScript, we can use the Math.hypot method.

For instance, we write

const distance = Math.hypot(endX - startX, endY - startY);

to call Math.hypot with difference of the x and y coordinates between the start and end points.

We get the x-coordinate difference with endX - startX.

And we get the y-coordinate difference with endY - startY.

Conclusion

To get distance between two points in canvas with JavaScript, we can use the Math.hypot method.

Sometimes, we want to detect when the mouse leaves the window with JavaScript.

In this article, we’ll look at how to detect when the mouse leaves the window with JavaScript.

How to detect when the mouse leaves the window with JavaScript?

To detect when the mouse leaves the window with JavaScript, we listen for the documentElement‘s mouseenter and mouseleave events.

For instance, we write

document.documentElement.addEventListener("mouseleave", () =>
  console.log("out")
);
document.documentElement.addEventListener("mouseenter", () =>
  console.log("in")
);

to call document.documentElement.addEventListener to listen for the mouseleave and mouseenter events.

If mouseleave event is triggered on documentElement then the mouse left the window.

If mouseenterevent is triggered on documentElement then the mouse comes into the window.

Conclusion

To detect when the mouse leaves the window with JavaScript, we listen for the documentElement‘s mouseenter and mouseleave events.

Sometimes, we want to add the equivalent of Ruby Array.any? in JavaScript.

In this article, we’ll look at how to add the equivalent of Ruby Array.any? in JavaScript.

How to add the equivalent of Ruby Array.any? in JavaScript?

To add the equivalent of Ruby Array.any? in JavaScript, we can use the array some method.

For instance, we write

const isBiggerThan10 = (element, index, array) => {
  return element > 10;
};

const hassBiggerThan10 = [2, 5, 8, 1, 4].some(isBiggerThan10);

to call [2, 5, 8, 1, 4].some with the isBiggerThan10 function to check if there’re any elements in [2, 5, 8, 1, 4] that’s bigger than 10 with isBiggerThan10.

It returns false since there’re no elements in [2, 5, 8, 1, 4] bigger than 10.

If there’re any elements bigger than 10, it’ll return true.

Conclusion

To add the equivalent of Ruby Array.any? in JavaScript, we can use the array some method.

Sometimes, we want to use module.exports as a constructor with Node.js.

In this article, we’ll look at how to use module.exports as a constructor with Node.js.

How to use module.exports as a constructor with Node.js?

To use module.exports as a constructor with Node.js, we export the constructor as a default export.

For instance, we write

class Square {
  constructor(width) {
    this.width = width;
  }
  area() {
    return this.width ** 2;
  }
}

export default Square;

to export the Square class as a default export with export default.

Then we import it by writing

import Square from "./square";

in another module in the same folder.

Conclusion

To use module.exports as a constructor with Node.js, we export the constructor as a default export.

Sometimes, we want to mock console when it is used by a third-party-library with Jest and JavaScript.

In this article, we’ll look at how to mock console when it is used by a third-party-library with Jest and JavaScript.

How to mock console when it is used by a third-party-library with Jest and JavaScript?

To mock console when it is used by a third-party-library with Jest and JavaScript, we call the jest.spyOn method.

For instance, we write

const consoleWarnMock = jest.spyOn(console, 'warn').mockImplementation();

to mock the console.warn method with the spyOn method in our test.

And then we call mockImplementation to return a mocked version of console.warn.

When we’re done with the test, then we call

consoleWarnMock.mockRestore();

to restore the original console.warn method.

Conclusion

To mock console when it is used by a third-party-library with Jest and JavaScript, we call the jest.spyOn method.