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What is " preventDefault"
preventDefault() is a function in JavaScript that is used to stop the default behavior of an event handler. It is commonly used with form submissions or link clicks to prevent the page from reloading or navigating to a new page.
Here is an example of how preventDefault() can be used with a link click event in JavaScript:
js Copy code
document.querySelector('a').addEventListener('click', function(event) {
event.preventDefault();
console.log('Link was clicked, but default behavior was prevented.');
});
In this example, the preventDefault() function is called within the event listener function to prevent the browser's default behavior of navigating to the linked page. Instead, clicking the link will only log a message to the console.
how to stop page from changing if user cancels prompt
You can stop a page from changing if a user cancels a prompt using the preventDefault() method. This is usually done in JavaScript using an onbeforeunload event attached to the window object. For example:
javascript Copy code
window.onbeforeunload = function() {
return "You cancelled the prompt";
};
Additionally, if you need to use a prompt to capture a value before a page unloads, you can use the prompt() method, which returns null if the user cancels the prompt. For example:
javascript Copy code
var value = prompt('Please enter a value before the page unloads');
if (value !== null) {
// do something with the value
}
function search(event) {
event.preventDefault();
let input = document.querySelector("#city-input");
console.log(search.value);
let h5 = document.querySelector("h5");
if (input.value) {
h5.innerHTML = `${input.value}...`;
} else {
h5.innerHTML = null;
alert(`${input.value}...`);
}
}
let form = document.querySelector("#search-form");
form.addEventListener("submit", search);The code is written in JavaScript and makes use of DOM-related functions, such as document.querySelector to access and manipulate elements of the DOM.
The search() function is being triggered when the user submits the form, indicated by the event listener form.addEventListener set to submit. The purpose of the function is to take the value from the input with the id="city-input" and store it. The event.preventDefault() is then used to actually prevent the form from submitting, since we want to manage the input with JavaScript logic first.
When the value is stored, a conditional is used to check whether the input is empty or not. If it is empty, an alert of the value will be triggered. Otherwise, the innerHTML of h5 is changed to the value of the input.
This is how the code works overall.
For more information on how events work in JavaScript, you can refer to this link.
Why do we need event.preventDefault();
event.preventDefault() is an important method used in the event handling of webpages. Calling event.preventDefault() will prevent the default behavior of an element from triggering, allowing more control over the flow of an application. For example, if you create a form on your page, calling event.preventDefault() on the form's submission will prevent the page from refreshing, allowing you to handle and process the form without causing the entire page to reload.
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