Author: John Au-Yeung

Sometimes, we want to set the focus to the first input element in an HTML form independent from the ID with JavaScript.

In this article, we’ll look at how to set the focus to the first input element in an HTML form independent from the ID with JavaScript.

How to set the focus to the first input element in an HTML form independent from the ID with JavaScript?

To set the focus to the first input element in an HTML form independent from the ID with JavaScript, we can use the document.forms property to get the form and the inputs inside the form.

For instance, we write

document.forms[0].elements[0].focus();

to get the first form with document.forms[0].

Then we use elements[0] to get the first element in the form.

Finally, we call focus on it to focus on the element.

Conclusion

To set the focus to the first input element in an HTML form independent from the ID with JavaScript, we can use the document.forms property to get the form and the inputs inside the form.

Sometimes, we want to insert a character after every n characters in JavaScript.

In this article, we’ll look at how to insert a character after every n characters in JavaScript.

How to insert a character after every n characters in JavaScript?

To insert a character after every n characters in JavaScript, we can use the string’s match and array join methods.

For instance, we write

const str = "123456789";
const parts = str.match(/.{1,3}/g);
const newValue = parts.join("-");

to call str.match with a regex that matches all groups of 3 digits and return the matches in an array.

Then we call join with '-' to join the matches text with '-'.

Conclusion

To insert a character after every n characters in JavaScript, we can use the string’s match and array join methods.

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.