Category: JavaScript Answers

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 do something when a user right-clicks on an element in our web app.

In this article, we’ll look at how to handle right-clicks with JavaScript.

Set the window.oncontextmenu Property to a Function

We can set the window.contextmenu property to an event handler function to listen for right clicks on the page.

To do this, we write:

window.oncontextmenu = (e) => {  
  e.preventDefault()  
  console.log('right clicked')  
}

We have the e parameter that has the right-click event object.

We call e.preventDefault to stop the default behavior for right clicks, which is to show the context menu on the page.

Once we called that, we can do anything we want in the rest of the function when the user right-clicks on the page.

Call the window.addEventListener Method to Add an Event Listener Function

Another way to do something when we right-click on the page is to call the window.addEventListener method to add an event listener function for listening to right clicks.

For instance, we can write:

window.addEventListener('contextmenu', (ev) => {  
  ev.preventDefault();  
  console.log('right clicked')  
});

We pass in the 'contextmenu' string to listen for context menu click events.

Then in the event listener, we call preventDefault the same way to stop the default right-click menu from displaying.

And then we can do what we want when the user right-clicks on the page.

Conclusion

We can listen for the contextmenu event and call preventDefault in the event handler function to run our own JavaScript when we right-click on the page.

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 get the names of the properties in a JavaScript object.

In this article, we’ll look at how to get a JavaScript object’s property names with JavaScript.

Using the Object.keys Method

We can use the Object.keys method to return an array of property name strings.

For instance, we can write:

const obj = {
  a: 1,
  b: 2,
  c: 3
}
Object.keys(obj).forEach(key => {
  console.log(key)
  console.log(obj[key])
})

We created the obj object with properties a , b , and c .

Then we call Object.keys with obj to return the property names of obj as strings.

Then we call forEach with a callback that has the key parameter with the key of the object being iterated through.

In the callback, we log the key and the value which we access with obj[key] .

Therefore, we get:

a
1
b
2
c
3

as the result.

Using the for-in Loop

We can get the object keys with the for-in loop.

For instance, we can write:

const obj = {
  a: 1,
  b: 2,
  c: 3
}
for (const key in obj) {
  console.log(key);
  console.log(obj[key]);
}

We get the object key from the key loop variable.

And then we get the key and value within the loop body the same way.

Therefore, we get:

a
1
b
2
c
3

as the result just like the previous example.

The for-in loop also loops through any properties inherited from prototype objects so we may get more keys than from the Object.keys method.

Object.keys only get property keys from non-inherited properties.

Conclusion

We can use the Object.keys method or the for-in loop to get the keys from a JavaScript object.

Sometimes, we want to disable an HTML button using JavaScript.

In this article, we’ll look at how to disable an HTML button using JavaScript.

Setting the disabled Property of a Button to true

To disable an HTML button using JavaScript, we can select the button and then set the disabled property of it.

For instance, if we have the following HTML:

<button>
  click me
</button>

Then we can select the button with document.querySelector and set its disabled property by writing:

document.querySelector("button").disabled = true;

Now we should see the button is disabled.

Use the setAttribute Method to set the disabled Attribute of a Button

Another way to set the disabled attribute of the button is to use the setAttribute method.

For instance, if we have the following HTML:

<button>
  click me
</button>

Then we can select the button with document.querySelector and set its disabled attribute with setAttribute by writing:

document.querySelector("button").setAttribute("disabled", "disabled");

We call setAttribute with the attribute name to set and the value to set it to as arguments respectively.

Also, we can write:

document.querySelector("button").setAttribute("disabled", true);

to set the disabled attribute top true to disable the button.

Conclusion

We can disable an HTML button with JavaScript by setting the disabled attribute of the selected button with JavaSceipt.