Author: John Au-Yeung

Sometimes, we want to alert for unsaved changes in form with JavaScript.

In this article, we’ll look at how to alert for unsaved changes in form with JavaScript.

Alert for Unsaved Changes in Form with JavaScript

To alert for unsaved changes in form with JavaScript, we can track changes done to inputs in a form.

Then we can set the window.onbeforeunload property to a function that checks the changing state of the input and returns an alert message if there’re changes.

For instance, if we have:

<div id="app">
  <input />
</div>

Then we can write the following JavaScript to track whether the input value has changed and shows the alert when the user leaves the page when there’re changes made:

let unsaved = false;

const input = document.querySelector("input");
input.addEventListener("change", () => {
  unsaved = true;
});

const unloadPage = () => {
  if (unsaved) {
    return "You have unsaved changes on this page.";
  }
};

window.onbeforeunload = unloadPage;

We have the unsaved variable, which we set to true in the change event listener of the input that we added with input.addEventListener .

And then we have the unloadPage function that checks if unsaved is true .

If it is, then we return a string that triggers the alert when we set the function as the value of window.onbeforeunload .

The message can’t be changed, so we can return any string.

onbeforeunload runs when we leave the page.

Conclusion

To alert for unsaved changes in form with JavaScript, we can track changes done to inputs in a form.

Then we can set the window.onbeforeunload property to a function that checks the changing state of the input and returns an alert message if there’re changes.

Sometimes, we want to paginate a JavaScript array.

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

Paginate a JavaScript Array

To paginate a JavaScript array, we can use the slice method to return the chunk of the array we want.

For instance, we can write:

const arr = Array(100).fill().map((_, i) => i)
const paginate = (array, pageSize, pageNumber) => {
  return array.slice((pageNumber - 1) * pageSize, pageNumber * pageSize);
}
console.log(paginate(arr, 10, 1))
console.log(paginate(arr, 10, 2))
console.log(paginate(arr, 10, 3))

We have the arr array with 100 entries.

Then we create paginate function that takes the array , pageSize and pageNumber parameters.

pageNumber starts from 1, so we call slice with (pageNumber — 1) * pageSize as the first argument and pageNumber * pageSize as the 2nd argument to return the slice according to a human-readable page number.

Then from the console log, we see:

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[10, 11, 12, 13, 14, 15, 16, 17, 18, 19]
[20, 21, 22, 23, 24, 25, 26, 27, 28, 29]

as the returned values of paginate with pageSize 10 and pageNumber 1, 2, and 3 respectively.

Conclusion

To paginate a JavaScript array, we can use the slice method to return the chunk of the array we want.

Sometimes, we want to create a JavaScript setInterval callback function that clears itself.

In this article, we’ll look at how to create a JavaScript setInterval callback function that clears itself.

Create a JavaScript setInterval Callback Function that Clears Itself

To create a JavaScript setInterval callback function that clears itself, we can call the clearInterval function with the timer handle as the argument.

For instance, we can write:

const myInterval = setInterval(() => {  
  console.log('hello')  
  clearInterval(myInterval);  
}, 50);

to call setInterval with a callback that logs 'hello' and then calls clearIntrval with the timer handle returned by setInterval to clear the timer.

The 2nd argument is set to 50 so that the callback runs every 50 milliseconds.

But the callback will only run once since we called clearInterval with myInterval to stop the timer.

Conclusion

To create a JavaScript setInterval callback function that clears itself, we can call the clearInterval function with the timer handle as the argument.

Sometimes, we want to get the entered value from the ACE editor and JavaScript.

In this article, we’ll look at how to get the entered value from the ACE editor and JavaScript.

Get the Entered Value from the ACE Editor and JavaScript

To get the entered value from the ACE editor and JavaScript, we can use the getValue method.

And to set the value of the editor, we can use the setValue method.

For instance, we can add the HTML for the editor by writing:

<script src="https://cdnjs.cloudflare.com/ajax/libs/ace/1.4.12/ace.js" integrity="sha512-GZ1RIgZaSc8rnco/8CXfRdCpDxRCphenIiZ2ztLy3XQfCbQUSCuk8IudvNHxkRA3oUg6q0qejgN/qqyG1duv5Q==" crossorigin="anonymous" referrerpolicy="no-referrer"></script>

<div id="editor" style="height: 200px; width: 200px">
  some text
</div>

Then we can write the following JavaScript code to get and set the editor value:

const editor = ace.edit("editor");
editor.setTheme("ace/theme/monokai");
editor.session.setMode("ace/mode/javascript");
const code = editor.getValue();
console.log(code)
editor.setValue("new code here");

We create the editor with:

const editor = ace.edit("editor");
editor.setTheme("ace/theme/monokai");
editor.session.setMode("ace/mode/javascript");

We call ace.edit with the ID of the element to use as the editor element.

Then we call editor.seesion.setMode to set the language mode.

Next, we call editor.getValue to get the value in the editor, which is 'some text‘ .

And the, we call editor.setValue with 'new code here' to replace the existing text with that in the editor.

Conclusion

To get the entered value from the ACE editor, we can use the getValue method.

And to set the value of the editor, we can use the setValue method.

Sometimes, we want to change the default text in Dropzone.js and JavaScript.

In this article, we’ll look at how to change the default text in Dropzone.js and JavaScript.

Change the Default Text in Dropzone.js and JavaScript

To change the default text in Dropzone.js and JavaScript, we can set the properties of the Dropzone.prototype.defaultOptions property.

For instance, we can create a drop zone by writing the following HTML:

<script src="https://rawgit.com/enyo/dropzone/master/dist/dropzone.js"></script>
<link rel="stylesheet" href="https://rawgit.com/enyo/dropzone/master/dist/dropzone.css">
<form action="/upload-target" class="dropzone"></form>

We add the dropzone.hs script and CSS. Then we add the form element to add the drop zone.

Next, we set the messages by writing:

Dropzone.prototype.defaultOptions.dictDefaultMessage = "Drop files here to upload";

Dropzone.prototype.defaultOptions.dictFallbackMessage = "Your browser does not support drag'n'drop file uploads.";

Dropzone.prototype.defaultOptions.dictFallbackText = "Please use the fallback form below to upload your files like in the olden days.";

Dropzone.prototype.defaultOptions.dictFileTooBig = "File is too big ({{filesize}}MiB). Max filesize: {{maxFilesize}}MiB.";

Dropzone.prototype.defaultOptions.dictInvalidFileType = "You can't upload files of this type.";

Dropzone.prototype.defaultOptions.dictResponseError = "Server responded with {{statusCode}} code.";

Dropzone.prototype.defaultOptions.dictCancelUpload = "Cancel upload";

Dropzone.prototype.defaultOptions.dictCancelUploadConfirmation = "Are you sure you want to cancel this upload?";

Dropzone.prototype.defaultOptions.dictRemoveFile = "Remove file";

Dropzone.prototype.defaultOptions.dictMaxFilesExceeded = "You can not upload any more files.";

All the messages are in the Dropzone.prototype.defaultOptions property.

Conclusion

To change the default text in Dropzone.js, we can set the properties of the Dropzone.prototype.defaultOptions property.