Category: JavaScript

Sometimes, we want to call removeEventListener with an anonymous function with JavaScript.

In this article, we’ll look at how to call removeEventListener with an anonymous function with JavaScript.

How to call removeEventListener with an anonymous function with JavaScript?

To call removeEventListener with an anonymous function with JavaScript, we assign the anonymous event listener function to a variable and call addEventListener and removeEventListener with the variable.

For instance, we write

const onScroll = () => {
  //...
};
document.body.addEventListener("scroll", onScroll, false);

setTimeout(() => {
  document.body.removeEventListener("scroll", onScroll, false);
}, 3000);

to call addEventListener to add the onScroll function as the scroll body element’s scroll event handler.

Then we call removeEventListener in the setTimeout callback that to remove the onScroll function as the body element’s scroll event handler.

Conclusion

To call removeEventListener with an anonymous function with JavaScript, we assign the anonymous event listener function to a variable and call addEventListener and removeEventListener with the variable.

Sometimes, we want to get value from object with default value with JavaScript.

In this article, we’ll look at how to get value from object with default value with JavaScript.

How to get value from object with default value with JavaScript?

To get value from object with default value with JavaScript, we can use the null coalescing operator.

For instance, we write

let foo = obj.maybeUndefined ?? "default value";

to use 'default value' as the fallback value for foo if obj.maybeUndefined is null or undefined.

The null coalescing operator is ??.

Conclusion

To get value from object with default value with JavaScript, we can use the null coalescing operator.

Sometimes, we want to call a JavaScript function recursively.

In this article, we’ll look at how to call a JavaScript function recursively.

How to call a JavaScript function recursively?

To call a JavaScript function recursively, we call the same function inside the function.

For instance, we write

const factorial = (n) => {
  if (n <= 1) {
    return 1;
  }
  return n * factorial(n - 1);
};

to define the factorial recursive function.

In it, we check if n is less than or equal to 1.

If it is, we return 1.

Otherwise, we return n multiplied by the result of factorial called with n - 1.

factorial is called until n is less than or equal to 1.

Conclusion

To call a JavaScript function recursively, we call the same function inside the function.

Sometimes, we want to convert Markdown to HTML with JavaScript.

In this article, we’ll look at how to convert Markdown to HTML with JavaScript.

How to convert Markdown to HTML with JavaScript?

To convert Markdown to HTML with JavaScript, we can use the showdown library.

For instance, we write

<script src="https://cdnjs.cloudflare.com/ajax/libs/showdown/2.1.0/showdown.min.js"></script>

to add the showdown library with a script tag.

Then we write

const converter = new showdown.Converter();
const text = "# hello, markdown!";
const html = converter.makeHtml(text);

to create a showdown.Converter convert object.

Then we call makeHtml on it with the Markdown text to convert it to html.

Conclusion

To convert Markdown to HTML with JavaScript, we can use the showdown library.