Category: JavaScript

Sometimes, we want to remove event listener with JavaScript.

In this article, we’ll look at how to remove event listener with JavaScript.

How to remove event listener with JavaScript?

To remove event listener with JavaScript, we can use the removeListener method.

For instance, we write

let clickCount = 0;

const onClick = (event) => {
  clickCount++;
  if (clickCount == 50) {
    canvas.removeEventListener("click", onClick);
  }
};

canvas.addEventListener("click", onClick);

to call removeListener with 'click' and onClick to remove the click listener.

We add the click listener by calling addEventListener with 'click' and onClick.

Conclusion

To remove event listener with JavaScript, we can use the removeListener method.

Sometimes, we want to check whether a script is running under Node.js.

In this article, we’ll look at how to check whether a script is running under Node.js.

How to check whether a script is running under Node.js?

To check whether a script is running under Node.js, we can check if window is undefined.

For instance, we write

if (typeof window === "undefined") {
  exports.foo = {};
} else {
  window.foo = {};
}

to check if window is undefined with typeof window === "undefined".

If it’s undefined, then the script isn’t running in the browser.

Conclusion

To check whether a script is running under Node.js, we can check if window is undefined.

Sometimes, we want to clear timeouts and intervals with React hooks.

In this article, we’ll look at how to clear timeouts and intervals with React hooks.

How to clear timeouts and intervals with React hooks?

To clear timeouts and intervals with React hooks, we call clearTimeout in the callback that we return in the useEffect hook callback.

For instance, we write

const Comp = () => {
  //...
  React.useEffect(() => {
    const timeoutID = window.setTimeout(() => {
      //...
    }, 1000);

    return () => window.clearTimeout(timeoutID);
  }, []);

  //...
};

to call useEffect with a callback that calls setTimout to run its callback with a 1 second delay.

Then we return a function that calls clearTimeout with the timeoutId returned by setInterval to clear the timer when the component unmounts.

Conclusion

To clear timeouts and intervals with React hooks, we call clearTimeout in the callback that we return in the useEffect hook callback.

Sometimes, we want to automatically set the focus to a textbox when a web page loads with JavaScript.

In this article, we’ll look at how to automatically set the focus to a textbox when a web page loads with JavaScript.

How to automatically set the focus to a textbox when a web page loads with JavaScript?

To automatically set the focus to a textbox when a web page loads with JavaScript, we can call the focus method on the text box in the window.onload handler.

For instance, we write

window.onload = () => {
  document.getElementById("Box1").focus();
};

to set window.onload to a function that runs when all the elements on the page are loaded.

In it, we get the text box with

document.getElementById("Box1")

And then we call focus on it.

Conclusion

To automatically set the focus to a textbox when a web page loads with JavaScript, we can call the focus method on the text box in the window.onload handler.

Sometimes, we want to check variable equality against a list of values with JavaScript.

In this article, we’ll look at how to check variable equality against a list of values with JavaScript.

How to check variable equality against a list of values with JavaScript?

To check variable equality against a list of values with JavaScript, we can use the array includes method.

For instance, we write

if ([1, 47, 28].includes(foo)) {
  // ...
}

to call [1, 47, 28].includes with foo to check if foo is one of 1, 47 or 28.

Conclusion

To check variable equality against a list of values with JavaScript, we can use the array includes method.