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JavaScriptAdvanced#performance#functions
JavaScriptIntermediate#dom#events
Difference between stopPropagation and preventDefault?
preventDefault cancels the browser's default action (form submit, link navigation) but the event keeps travelling. stopPropagation stops the event reaching other elements but the default action still happens.
Example
form.addEventListener('submit', e => {
e.preventDefault(); // stay on the page
save();
});