Category: JavaScript Answers

Sometimes, we want to use map() on an array in reverse order with JavaScript.

In this article, we’ll look at how to use map() on an array in reverse order with JavaScript.

How to use map() on an array in reverse order with JavaScript?

To use map() on an array in reverse order with JavaScript, we can use the array reverse method.

For instance, we write

const reversed = myArray
  .slice(0)
  .reverse()
  .map((a) => {
    //...
  });

to call myArray with slice to make a copy of the array.

Then we can reverse to reverse the copied array.

Next, we call map with a callback to map the reversed array’s values to the ones we want.

Conclusion

To use map() on an array in reverse order with JavaScript, we can use the array reverse method.

Sometimes, we want to fix jasmine: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL error with JavaScript.

In this article, we’ll look at how to fix jasmine: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL error with JavaScript.

How to fix jasmine: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL error with JavaScript?

To fix jasmine: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL error with JavaScript, we should make sure done is called when async code is finished running.

For instance, we write

it("should work", (done) => {
  //...
});

it("should work", () => {
  //...
});

to get the done function in the parameter of the first test.

And we should call it after async code is run in the first test if there’s any.

Conclusion

To fix jasmine: Async callback was not invoked within timeout specified by jasmine.DEFAULT_TIMEOUT_INTERVAL error with JavaScript, we should make sure done is called when async code is finished running.

Sometimes, we want to check if two arrays have the same values with JavaScript.

In this article, we’ll look at how to check if two arrays have the same values with JavaScript.

How to check if two arrays have the same values with JavaScript?

To check if two arrays have the same values with JavaScript, we can use the array every method.

For instance, we write

const set1 = new Set(arr1);
const set2 = new Set(arr2);
return (
  arr1.every((item) => set2.has(item)) && arr2.every((item) => set1.has(item))
);

to convert arrays arr1 and arr2 to sets.

And then we call arr1.every with a callback to see if set2 has the item in arr1.

Then we call arr2.every with a callback to see if set1 has the item in arr2.

If both every call return true, then both arrays have the same values.

Conclusion

To check if two arrays have the same values with JavaScript, we can use the array every method.

Sometimes, we want to merge two JavaScript objects together in ES6+.

In this article, we’ll look at how to merge two JavaScript objects together in ES6+.

How to merge two JavaScript objects together in ES6+?

To merge two JavaScript objects together in ES6+, we use the object spread syntax.

For instance, we write

const merged = { ...obj1, ...obj2 };

to merge the properties of obj1 and obj2 into a new object.

A shallow copy of obj1 and obj2 are made before their contents are put in the new object.

Conclusion

To merge two JavaScript objects together in ES6+, we use the object spread syntax.

Sometimes, we want to put a clear button inside a HTML text input box.

In this article, we’ll look at how to put a clear button inside a HTML text input box.

How to put a clear button inside a HTML text input box?

To put a clear button inside a HTML text input box, we add an input with type attribute set to search.

For instance, we write

<input type="search" placeholder="Search..." />

to add the input with type set to search to make the clear button show on the right end of the input box.

Conclusion

To put a clear button inside a HTML text input box, we add an input with type attribute set to search.