How to listen to close button events in JavaScript

JavaScript is one of the powerful tools of client-side programming, which can be used to add various functions and interactivity to improve the user experience of the website. The close button is an important element in web applications. In this article, we will discuss how to listen to the close button event in JavaScript and use it to add functionality to your application.

The close button is a button set in the upper right corner of the browser window. When the user clicks this button, the currently open window or tab will be closed and the current process will end. Close buttons are commonly used in web applications and browser extensions.

Use JavaScript to listen to the close button event

Let us first take a look at how to use JavaScript to listen to the close button event. In JavaScript, we use the window.onbeforeunload event listener to detect the click event of the close button. The onbeforeunload event is fired just before the window, tab, or browser is closed. We can add the functionality we want to perform in the callback function of the event.

The following are common usages:

window.onbeforeunload = function() {
  // 您想要运行的功能
};

In the above code, we set an anonymous function as the callback function of the window.onbeforeunload event. In the function, we can add any operations, such as opening a new window, reminding the user to save data, etc.

Perform operations in callback functions

Now, let’s look at a specific example. Let's say we are building an online shopping application and we need to make sure the customer has saved their shopping cart before they leave the page or click the close button. To achieve this, we can use the following code:

window.onbeforeunload = function() {
  const cart = JSON.parse(localStorage.getItem("shoppingCart"));
  if (cart.length > 0) {
    alert("请确保您已保存购物车！");
  }
};

In this code, we first use localStorage to get the contents of the shopping cart. In the callback function, we use an if statement to check if there is an item in the shopping cart. If there are items in the cart, we display a reminder window to the user to prompt them to make sure they have saved their cart.

Note: When you attach a function on the onbeforeunload event, the browser notifies the user that it is trying to close the window and asks them if they are sure to leave. The user has the option to stay on the page or continue closing the window. If you don't add it in the onbeforeunload event callback function, the event will not fire.

This event also applies to closing the browser tab. Just use the onbeforeunload event in the page. This event will only be triggered when the user leaves the page.

Summary

In this article, we discussed how to listen to close button events in JavaScript and add functionality to your web application. We use the window.onbeforeunload event listener to monitor the event and perform the required actions in the callback function. Additionally, when you attach a function on the onbeforeunload event, the browser notifies the user that an attempt is being made to close the window and asks them if they are sure to leave.

Remember, when using the onbeforeunload event, make sure your code does not interfere with or interrupt the user's browsing experience. Think carefully about how your users will feel before you try to add functionality.

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