Category: jQuery

To validate that a form with multiple checkboxes to have at least one checked with jQuery, we can call the serializeArray method on the selected checkboxes to see how many of them are checked.

For instance, if we have the following form:

<form>
  <fieldset id="cbgroup">
    <div><input name="list" id="list0" type="checkbox" value="newsletter0">zero</div>
    <div><input name="list" id="list1" type="checkbox" value="newsletter1">one</div>
    <div><input name="list" id="list2" type="checkbox" value="newsletter2">two</div>
  </fieldset>

  <input name="submit" type="submit" value="submit">
</form>

Then we can check how many checkboxes are checked by writing:

const onSubmit = (e) => {
  e.preventDefault()
  const fields = $("input[name='list']").serializeArray();
  if (fields.length === 0) {
    console.log('nothing selected');
    return false;
  } else {
    console.log(fields.length, "items selected");
  }
}

document.forms[0].addEventListener('submit', onSubmit)

We have the onSubmit function that’s used as the submit handler of the form.

In the function, we call e.preventDefault to prevent the server-side submission behavior.

Then we call $("input[name='list']").serializeArray() to return an array of checked checkboxes and assign it to fields.

Therefore, if fields.length is 0, then nothing is checked.

Otherwise, at least some checkboxes are checked.

To add DOM elements with jQuery, we can use the jQuery appendTo method.

For instance, if we want to add an anchor element to the body element, we write:

$("<a/>", {
  id: 'link',
  href: 'http://www.example.com/',
  text: 'Example Page'
}).appendTo("body");

We call $ with '<a/>' to create a new element.

The 2nd argument we passed into $ are the attributes and the values of the element.

Then we call appendTo on the returned object with 'body' to attach the element to body.

Sometimes, we want to get the context of a Canvas with jQuery

In this article, we’ll look at how to get the context of a Canvas with jQuery.

Get the Context of a Canvas with jQuery

To get the context of a Canvas with jQuery, we call the get method with the index of the element we want to get.

Then we can call getContext on the returned element.

For instance, if we have the following canvas:

<canvas width='200' height='200'></canvas>

We write:

const ctx = $("canvas").get(0).getContext('2d');  
console.log(ctx)

to select canvas elements with $(“canvas”) .

Then we use get(0) to get the first canvas element selected.

And then we call getContext on that to get the context.

Conclusion

To get the context of a Canvas with jQuery, we call the get method with the index of the element we want to get.

Then we can call getContext on the returned element.

To handle tab key presses in a text area with jQuery, we can detect when the tab key is pressed in the text area.

Then if it’s pressed, we can call e.preventDefault on it to prevent the default behavior.

For instance, if we have the following text area:

<textarea></textarea>

Then we can listen to the keydown event to listen for tab key presses:

$("textarea").keydown((e) => {
  if (e.keyCode === 9) {
    const start = e.target.selectionStart;
    const end = e.target.selectionEnd;
    const $this = $(e.target);
    const value = $this.val();
    $this.val(`${value.substring(0, start)}\t${value.substring(end)}`);
    $this.selectionStart = $this.selectionEnd = start + 1;
    e.preventDefault();
  }
});

We get the text area with $(“textarea”) .

Then we call keydown to listen to the keydown event.

We pass in a callback to the keydown method.

In the callback, we check e.keyCode to check if it’s 9 to see if we pressed on tab or not.

If it’s true , then we pressed on tab.

In the if block, we get the start and end of the text selection with:

const start = e.target.selectionStart;
const end = e.target.selectionEnd;

Then assign the textarea element to $this with:

const $this = $(e.target);

We get the input value wit:

const value = $this.val();

And then we update the value of the text area by writing:

$this.val(`${value.substring(0, start)}t${value.substring(end)}`);

to insert a tab at the position where the selection is made.

Finally, we set the selection range with:

$this.selectionStart = $this.selectionEnd = start + 1;

to move the cursor to the end.

And finally, we call e.preventDefault to stop the default behavior, which is to move focus away from the text area.

To disable right-click on images using jQuery, we can listen to the contextmenu event on the image element.

Then in the event handler callback, we can return false to prevent right-clicks on images.

For instance, if we have the following image:

<img src='https://picsum.photos/200/300'>

Then we can write:

$('img').bind('contextmenu', (e) => {  
  return false;  
});

to get all image elements with $(‘img’) .

Then we call bind with 'contextmenu' to listen to the contextmenu event.

And in the event handler callback, we return false .

Now when we right-click on the image, we shouldn’t see any context menu displayed.