Category: JavaScript Answers

Sometimes, we want to remove all properties from a object with JavaScript.

In this article, we’ll look at how to remove all properties from a object with JavaScript.

How to remove all properties from a object with JavaScript?

To remove all properties from a object with JavaScript, we can loop through each property and use delete to delete them.

For instance, we write

Object.keys(object).forEach((key) => delete object[key]);

to call Object.keys with object to get all string non-inherited keys in object as an array.

Then we call forEach with a callback to delete each property with delete.

Conclusion

To remove all properties from a object with JavaScript, we can loop through each property and use delete to delete them.

To mock a constructor like new Date() with Jest and JavaScript, we can use the setSystemTime method.

For instance, we write

beforeAll(() => {
  jest.useFakeTimers("modern");
  jest.setSystemTime(new Date(2022, 3, 1));
});

afterAll(() => {
  jest.useRealTimers();
});

to call useFakeTimers to use a mock timer.

Then we call setSystemTime to set the date and time in the test environment.

We make the calls in the beforeAll callback to run the code before any tests are run.

Then in the afterAll callback, we call useRealTimers to clear the mocked timers and use the real ones.

Conclusion

To mock a constructor like new Date() with Jest and JavaScript, we can use the setSystemTime method.

Sometimes, we want to convert timestamp to relative time with JavaScript.

In this article, we’ll look at how to convert timestamp to relative time with JavaScript.

How to convert timestamp to relative time with JavaScript?

To convert timestamp to relative time with JavaScript, we use the Intl.RelativeTimeFormat constructor.

For instance, we write

const units = [
  ["year", 31536000000],
  ["month", 2628000000],
  ["day", 86400000],
  ["hour", 3600000],
  ["minute", 60000],
  ["second", 1000],
];

const rtf = new Intl.RelativeTimeFormat("en", { style: "narrow" });
const relatime = (elapsed) => {
  for (const [unit, amount] of units) {
    if (Math.abs(elapsed) > amount || unit === "second") {
      return rtf.format(Math.round(elapsed / amount), unit);
    }
  }
};

to create the rtf RelativeTimeFormat object.

Then we define the relatime function that takes the elapsed relative in milliseconds.

And then we use a for-of loop to loop through the units array.

In the loop, we check if the absolute elapsed amount is bigger than amount or the unit is 'second'.

If either are true, then we return the formatted elapsed time we get with rtf.format to format the elapsed time to the unit.

Conclusion

To convert timestamp to relative time with JavaScript, we use the Intl.RelativeTimeFormat constructor.

Sometimes, we want to find element index in container with JavaScript.

In this article, we’ll look at how to find element index in container with JavaScript.

How to find element index in container with JavaScript?

To find element index in container with JavaScript, we can use the spread operator and the indexOf method.

For instance, we write

const index = [...el.parentElement.children].indexOf(el);

to use el.parentElement.children to get all the child elements of the el element’s parent element.

Then we spread the node list to an array.

Next, we call indexOf with el to get the index of el in the array of elements.

Conclusion

To find element index in container with JavaScript, we can use the spread operator and the indexOf method.

Sometimes, we want to wait until page is completely loaded with Puppeteer and JavaScript.

In this article, we’ll look at how to wait until page is completely loaded with Puppeteer and JavaScript.

How to wait until page is completely loaded with Puppeteer and JavaScript?

To wait until page is completely loaded with Puppeteer and JavaScript, we call goto with an object with the waitUntil property.

For instance, we write

await page.goto(url, { waitUntil: "domcontentloaded" });

to call page.goto with the url and { waitUntil: "domcontentloaded" } to navigate to the url and wait until the whole page is loaded by setting waitUntil to 'domcontentloaded'.

Conclusion

To wait until page is completely loaded with Puppeteer and JavaScript, we call goto with an object with the waitUntil property.