Category: JavaScript Answers

Sometimes, we want to change the 1-24 hour return from the JavaScript date’s getHours method to a 1-12 hour.

In this article, we’ll look at how to change the 1-24 hour return from the JavaScript date’s getHours method to a 1-12 hour.

How to change the 1-24 hour return from the JavaScript date’s getHours method to a 1-12 hour?

To change the 1-24 hour return from the JavaScript date’s getHours method to a 1-12 hour, we can use the % operator.

For instance, we write:

const hours12 = (date) => {
  return (date.getHours() + 24) % 12 || 12;
}

const d = new Date('December 25, 2022 23:15:30')
console.log(hours12(d))

We define the hours12 to return the hours of the date in 12 hour format instead of 24.

In the function, we call date.getHours to get the hours, which is between 1 and 24.

Then we convert it to 12 hour format by adding 24 and then use the % to get the remainder when the result is divided by 12.

If the remainder is 0, then we return 12.

Therefore, the console log should log 11.

Conclusion

To change the 1-24 hour return from the JavaScript date’s getHours method to a 1-12 hour, we can use the % operator.

Sometimes, we want to format datetime in JavaScript.

In this article, we’ll look at how to format datetime in JavaScript.

How to format datetime in JavaScript?

To format datetime in JavaScript, we can use the moment.js’ format method.

For instance, we write:

<script src="https://cdnjs.cloudflare.com/ajax/libs/moment.js/2.29.1/moment.min.js"></script>

to add the moment script.

Then we write:

const s = moment("2022-01-17T08:44:29+0100").format('MM/DD/YYYY');
console.log(s)

to call moment with a datetime string to create a moment object.

Then we call format on it with a format string to format it in the format specified.

Therefore, s is '01/16/2022'.

Conclusion

To format datetime in JavaScript, we can use the moment.js’ format method.

Sometimes, we want to prevent middle mouse click scrolling with JavaScript.

In this article, we’ll look at how to prevent middle mouse click scrolling with JavaScript.

How to prevent middle mouse click scrolling with JavaScript?

To prevent middle mouse click scrolling with JavaScript, we can listen to the mousedown event on the body element.

Then we check if the middle mouse button is clicked and prevent the default scrolling behavior if it is.

For instance, we write:

document.body.onmousedown = (e) => {
  if (e.button === 1) {
    e.preventDefault();
    return false;
  }
}

We set document.body.onmousedown to a function that checks if the middle mouse button is clicked.

We do that checking if e.button is 1.

If it is, then we call e.preventDefault and return false to prevent the default scrolling behavior.

Conclusion

To prevent middle mouse click scrolling with JavaScript, we can listen to the mousedown event on the body element.

Then we check if the middle mouse button is clicked and prevent the default scrolling behavior if it is.

Sometimes, we want to make a HTML5 datalist visible when focus event fires on input with JavaScript.

In this article, we’ll look at how to make a HTML5 datalist visible when focus event fires on input with JavaScript.

How to make a HTML5 datalist visible when focus event fires on input with JavaScript?

To make a HTML5 datalist visible when focus event fires on input with JavaScript, we can save the old input value on mouse move. On mouse down, we can empty the input value. And on mouse up, we set the input value to the saved input value.

For instance, we write:

<input name="input" list="input" />

<datalist id="input">
  <option value="apple" selected></option>
  <option value="orange"></option>
  <option value="grape"></option>
</datalist>

to add an input and datalist associated with the input.

Then we write:

const input = document.querySelector('input')
let old;
input.onmousemove = (e) => {
  e.target.focus()
  old = e.target.value
}

input.onmousedown = (e) => {
  e.target.value = ''
}

input.onmouseup = (e) => {
  e.target.value = old
}

to select the input and define the old variable to store the old value.

The we focus on the input and save the old value on mouse move with:

input.onmousemove = (e) => {
  e.target.focus()
  old = e.target.value
}

Then on mouse down, we empty the input value with:

input.onmousedown = (e) => {
  e.target.value = ''
}

Then on mouse up, we set the input value to the saved old value with:

input.onmouseup = (e) => {
  e.target.value = old
}

Conclusion

To make a HTML5 datalist visible when focus event fires on input with JavaScript, we can save the old input value on mouse move. On mouse down, we can empty the input value. And on mouse up, we set the input value to the saved input value.

Sometimes, we want to disable or enable submit button until all forms have been filled with JavaScript.

In this article, we’ll look at how to disable or enable submit button until all forms have been filled with JavaScript.

How to disable or enable submit button until all forms have been filled with JavaScript?

To disable or enable submit button until all forms have been filled with JavaScript, we can set the disabled property according to the input values.

For instance, we write:

<form name="theForm">
  <input type="text" />
  <input type="text"  />
  <input id="submitbutton" type="submit" disabled />
</form>

We have a form that has 2 text inputs and a submit button.

Then to enable the submit button only when all the text inputs are filled, we write:

document.onkeyup = (e) => {
  if (e.target.tagName === 'INPUT') {
    const canSubmit = [...document.forms.theForm.querySelectorAll('input[type="text"]')]
      .every(i => {
        return i.value
      })
    document.forms.theForm.querySelector('input[type="submit"]').disabled = !canSubmit
  }
}

We set the document.onkeyup function to a function that checks if the keyup event is triggered by an input element.

If it is, then we check if all the text inputs are filled with:

const canSubmit = [...document.forms.theForm.querySelectorAll('input[type="text"]')]
  .every(i => {
    return i.value
  })

Then we set the disabled attribute of the submit button with:

document.forms.theForm.querySelector('input[type="submit"]').disabled = !canSubmit

Now the submit button is only enabled when all the text inputs are filled.

Conclusion

To disable or enable submit button until all forms have been filled with JavaScript, we can set the disabled property according to the input values.