Category: JavaScript

Sometimes, we want to check whether dynamically attached event listener exists or not with JavaScript.

In this article, we’ll look at how to check whether dynamically attached event listener exists or not with JavaScript.

How to check whether dynamically attached event listener exists or not with JavaScript?

To check whether dynamically attached event listener exists or not with JavaScript, we can get and set the element’s listener attribute.

For instance, we write

export const attachEvent = (
  element: Element,
  eventName: string,
  callback: () => void
) => {
  if (element && eventName && element.getAttribute("listener") !== "true") {
    element.setAttribute("listener", "true");
    element.addEventListener(eventName, () => {
      callback();
    });
  }
};

to get the listener attribute with element.getAttribute("listener").

If it’s set to 'true', then the listener is attached.

Otherwise, we attach it with addEventListener and call setAttribute to set the listener attribute to true.

Then we use it like

attachEvent(domElement, "click", listenerFunc)

by calling it with the element, event name, and event handler function.

Conclusion

To check whether dynamically attached event listener exists or not with JavaScript, we can get and set the element’s listener attribute.

Sometimes, we want to change the content of a text area with JavaScript.

In this article, we’ll look at how to change the content of a text area with JavaScript.

How to change the content of a text area with JavaScript?

To change the content of a text area with JavaScript, we can set the value property of it.

For instance, we write

document.getElementById('myTextarea').value = '';

to select the text area with ID myTextArea with getElementById.

And then we set its value property to an empty string to empty the text area.

The text area is something like

<textarea id="myTextarea">foobar</textarea>

Conclusion

To change the content of a text area with JavaScript, we can set the value property of it.

Sometimes, we want to get element inside element by class and ID with JavaScript.

In this article, we’ll look at how to get element inside element by class and ID with JavaScript.

How to get element inside element by class and ID with JavaScript?

To get element inside element by class and ID with JavaScript, we can get the parent element.

And then we call the method to select the child element in the parent.

For instance, we write

const targetDiv = document
  .getElementById("foo")
  .getElementsByClassName("bar")[0];

to call getElementById to get the parent element with ID foo.

Then we call getElementsByClassName with 'bar' to select the elements with class bar in the element with ID foo.

Conclusion

To get element inside element by class and ID with JavaScript, we can get the parent element.

And then we call the method to select the child element in the parent.

Sometimes, we want to find variable type in JavaScript.

In this article, we’ll look at how to find variable type in JavaScript.

How to find variable type in JavaScript?

To find variable type in JavaScript, we can use the typeof operator.

For instance, we write

typeof "foo"

to return 'string' since 'foo' is a string.

We can use this with other primitive values like numbers and booleans. It also works with functions.

Conclusion

To find variable type in JavaScript, we can use the typeof operator.