Category: JavaScript Answers

Sometimes, we want to remove a leading comma from a JavaScript string.

In this article, we’ll look at how to remove a leading comma from a JavaScript string.

Using the String.prototype.substring Method

We can use the JavaScript string substring method to get the part of a string.

Therefore, we can use it to return a string without the leading comma.

For instance, we can write:

const myOriginalString = ",'first string','more','even more'";
const newString = myOriginalString.substring(1);
console.log(newString)

We call substring with 1 to return a string the part of myOriginalString from index 1 to the end.

Therefore, newString is "’first string’,’more’,’even more’” .

Using the String.prototype.split Method

We can use the JavaScript string split method to split a string by a separator string.

For instance, we can write:

const myOriginalString = ",'first string','more','even more'";
const [_, ...rest] = myOriginalString.split(',');
const newString = rest.join(',')
console.log(newString)

We call split with ',' to split myOriginalString by the comma.

Then we use the rest operator to get a string array with anything but the first comma.

And then we call join with ',' to join the strings in rest with the comma.

And so newString has the same value as before.

Using the String.prototype.replace Method

Another way to remove the leading commas from a string is to use the JavaScript string’s replace method.

For example, we can write:

const myOriginalString = ",'first string','more','even more'";
const newString = myOriginalString.replace(/^,/, '');
console.log(newString)

We call replace with /^,/ to replace the leading comma with an empty string.

And so newString is the same as before.

Conclusion

We can use various string methods to get rid of the leading comma from a string.

Sometimes, we want to let users clear an HTML file input with JavaScript.

In this article, we’ll look at how to clear an HTML file input with JavaScript.

Setting the value Property of the File Input to an Empty String

We can set the value property of the file input to an empty string.

For instance, if we have the following HTML code:

<input type='file'>  
<button>  
  clear  
</button>

Then we can write:

const input = document.querySelector('input')  
const button = document.querySelector('button')  
button.addEventListener('click', () => {  
  input.value = '';  
})

to clear the file input when we click on the clear button.

We get the input and the button with document.querySelector .

Then we call addEventListener on the button with the 'click' string as the first argument to listen for clicks on the button.

In the event handler, we just set input.value to an empty string.

Then when we select a file for the input and click clear, we see that the selected file is gone.

We can also set value to null to do the same thing.

Conclusion

We can clear the file input with JavaScript by setting the value property of the file input to an empty string or null .

Sometimes, we want to convert a JavaScript array into a set.

In this article, we’ll look at how to convert a JavaScript array to a set.

Create a Set with the JavaScript Set Constructor

We can use the JavaScript Set constructor to create a JavaScript set from an array.

For instance, we can write:

const array = [{
    name: "malcom",
    dogType: "golden retriever"
  },
  {
    name: "peabody",
    dogType: "bulldog"
  },
  {
    name: "pablo",
    dogType: "chihuahua"
  }
];
const namesSet = new Set(array.map(d => d.name));
console.log(namesSet)

We have an array array with an array of objects.

We want to create a set with the name value from each object.

To do this, we call array.map with a callback to return the name property of each object.

We then pass the returned names string array into the Set constructor to create the set.

Therefore namesSet is a set with “malcom”, “peabody”, and “pablo” in it.

Passing the array into the Set constructor will remove the duplicate values if there are any in the set.

Conclusion

We can use the JavaScript Set constructor to create a set from an array.

Sometimes, we want to convert a Unix timestamp to a calendar date with Moment.js and JavaScript.

In this article, we’ll look at how to convert a Unix timestamp to a calendar dare with moment.js and JavaScript.

Use the unix and format Methods

We can use the unix method to create a moment object from a timestamp.

Then we can use the format method to format the date into a calendar date.

For instance, we can write:

import moment from 'moment'  
const dt = +new Date(2021,1,1)  
const dateString = moment.unix(dt / 1000).format("MM/DD/YYYY");  
console.log(dateString)

We create the dt date object with the Date constructor.

Then we convert it to a timestamp in milliseconds with the unary + operator.

Next, we call moment.unix with a timestamp in seconds.

And then we call format to format the date into MM/DD/YYYY format.

And so dateString is ‘02/01/2021’ .

Use the moment Function and the format Method

We can just use the moment function without the unix method to create a moment object from a timestamp.

For instance, we can write:

import moment from 'moment'  
const dt = +new Date(2021,1,1)  
const dateString = moment(dt).format("MM/DD/YYYY");  
console.log(dateString)

The moment function takes a timestamp in milliseconds.

Therefore, we don’t have to divide dt by 1000 when we pass it in.

The rest of the code is the same and we get the same result as before.

Conclusion

We can convert a timestamp to a calendar date with format with the moment function or the unix method with the format method.

Sometimes, we want to get the scrollbar size of an element with JavaScript.

In this article, we’ll look at how to get the size of the scrollbar that’s part of a scrollable element with JavaScript.

Use the getBoundingClientRect Method and the scrollHeight Property with JavaScript

We can get the element’s scrollbar size with the getBoundingClientRect method and the scrollHeight property of an element with JavaScript.

To do this, we subtract the height property value retuned by getBoundingClientRect method by the scrollHeight property’s value to get the width of the horizontal scrollbar.

For instance, if we have:

<div id="app" style='width: 100px; overflow-x: scroll'></div>

Then we can add elements to the div and get the horizontal scrollbar height by writing:

const app = document.querySelector('#app')
for (let i = 0; i < 100; i++) {
  const span = document.createElement('span')
  span.textContent = i
  app.appendChild(span)
}

const getScrollbarHeight = (el) =>{
  return el.getBoundingClientRect().height - el.scrollHeight;
};
console.log(getScrollbarHeight(app))

We get the div with querySelector .

Then we add some spans into the div.

The div has width set and overflow-x set to scroll.

This means the div should have a horizontal scrollbar.

Next, we create the getScrollbarHeight function that subtracts the height from getBoundingClientRect by the scrollHeight , which gives us the height of the horizontal scrollbar.

Then we log the scrollbar height with console log.

Likewise, we can get the scrollbar width with:

<div id="app" style='height: 100px; overflow-y: scroll'></div>

and:

const app = document.querySelector('#app')
for (let i = 0; i < 100; i++) {
  const p = document.createElement('p')
  p.textContent = i
  app.appendChild(p)
}

const getScrollbarHeight = (el) =>{
  return el.getBoundingClientRect().width - el.scrollWidth;
};
console.log(getScrollbarHeight(app))

We add p elements into a div that’s scrollable vertically.

Instead of subtracting the heights, we subtract the widths.

And we should get the scrollbar width from the console log.

Conclusion

We can get the scrollbar width and height by calling the getBoundingClientRect method and the scroll width or height and getting the difference between the 2.