Updated March 30, 2023
Introduction to JavaScript onunload
JavaScript onunload is an event that occurs when the user tries to load some page, and the page remains in the stuck state means it remains unloaded. There might be a chance that the onunload event could also occur when the browser has been closed while loading the page. Onunload event primarily reaches the state of onunload when the user navigates away from the page while clicking, submitting, and closing the browser window. This event also occurs when a user tries to reload a web page and access information while loading.
Syntax
object.onunload = function()
{
JavaScript Body;
};The syntax flow is as follows where the object calls for the onunload event at the time of execution of the script and then calls for the onunload function of the JavaScript.
How does onunload event work in JavaScript?
Events are the occurrences that mostly get caused due to the unnecessary action performed at the time of implementing any function or trying to perform some other action but navigates and then gets some other unproductive output. Even when compared to the real-life scenario, the same thing happens, which involves trying to attempt and get some value but then ends up getting some other value. onunload also occurs when the user navigates and ends up landing on some unwanted pages, but still, the page tries to load itself but gets hanged due to two threads running parallelly to achieve the activity of loading and unloading.
It happens when the user tries to click any link, submit a form, or close any browser in the window that is not supposed to be. So let’s get into the real-life events; suppose, for an instance, a programmer tries to create a Graphical User Interface which involves many menu’s and forms to submit and then tries to enhance the entire UI then what happens is that at the time of modification or enhancement programmers navigates away from the main components and then tries to get into the loading of files and observes that the event of loading the web page at the time of clicking the link or at the time of submitting the form for testing and verifying the component gets failed.
These events in JavaScript, which are unwanted but occurs frequently due to the unwanted actions performed by the programmers, leads to onunload events wherein the situation becomes quite cumbersome as the programmer needs to solve the modification comes out of the hanging situation and then performs the entire action in the remaining part of the processing. Therefore, when these events get compared to the real-life gets relatable and thus helps in getting the essence of the events how they can make the user realize each of the components or say each of the enhancement and modifications in the JavaScript for further usage.
The events in case of JavaScript support for all kinds of browsers like google chrome with the highest prioritized browser with the user compatibility with the events and other attributes related to the performance of activities like onunload. So it might get possible that due to some different browser settings, the events may get hindered and the behavior of all the other events might also get hampered if not properly used, and the event also might not work properly as expected.
There are some event objects which as part of the JavaScript onunload function, may use the properties and methods for its working; hence all the other event objects which are part of this JavaScript onunload event may include objects like MouseEvent and KeyBoard Event that can access to any event object anytime and anywhere. When incorporated to the event object in unison, some of the HTML Data Objects form the manipulated event objects for the events and the functions in work.
Most of the events are normally used for testing and verification before the user initiates a trigger, such as at the time of clicking any link using a mouse for verification. Therefore, most of the event types, including the abort, afterprint, beforeprint, etc., are responsible for triggering the event object. The obvious point that must be remembered is that both the event object and a data object, when incorporated with the function within the JavaScript, will make JavaScript onunload possible.
Examples of JavaScript onunload
Different examples are mentioned below:
Example #1
This program demonstrates the onunload function in JavaScript where the user makes use of the onunload function and then tries to call the web-page for its function and then tries to close the window to verify the reloading of the function using the script and then assigns an alert function with the script as shown in the output.
Code:
<!DOCTYPE html>
<html>
<body onunload="One_Func()">
<h1>Hello Everyone Welcome to the web-page</h1>
<p>Lets close the window for reloading a page. </p>
<p><strong>Caution:</strong> Due to some different settings in the browser it is needed to get the browser compatibility proper. </p>
<script>
function One_Func() {
alert("Thanks for visiting the web-page");
}
</script>
</body>
</html>Output:
Example #2
This program demonstrates the onload functionality as part of the event object, which is also somewhat responsible for the onunload function of JavaScript as it tries to load a web page and then asks for the function to call the web page and then on calling the trail function throws an alert for loading the entire page once click on the ok button as shown in the output it displays and loads the file for proper viewing.
Code:
<!DOCTYPE html>
<html>
<body onload="trial_func()">
<h1>Welcm Everyone!</h1>
<script>
function trial_func() {
alert("Loading _Page");
}
</script>
</body>
</html>Output:
Conclusion
JavaScript Onunload is one of the very important events which must be kept a constant check on. These functions with the events involve lots of events and objects that get executed accordingly and should also include a proper flow and sync within the components. Thus, only they can work seamlessly for the desired working.
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