js method to detect whether form data changes when leaving or refreshing a page

This article example describes how JS detects whether form data changes when leaving or refreshing a page. Share it for your reference, as follows:

 function formIsDirty(form) { for (var i = 0; i < form.elements.length; i++) { var element = form.elements[i]; var type = element.type; if (type == "checkbox" || type == "radio") { if (element.checked != element.defaultChecked) { return true; } } else if (type == "hidden" || type == "password" || type == "text" || type == "textarea") { if (element.value != element.defaultValue) { return true; } } else if (type == "select-one" || type == "select-multiple") { for (var j = 0; j < element.options.length; j++) { if (element.options[j].selected != element.options[j].defaultSelected) { return true; } } } return false;}window.onbeforeunload = function (e) { e = e || window.event; if (formIsDirty(document.forms["someForm"])) { // IE and Firefox if (e) { e.returnValue = "Sorry, the page data has been modified, not saved yet, I'm sure you want to refresh or leave this page?"; } // Safari browser returns "Sorry, the page data has been modified, not saved yet, I'm sure you want to refresh or leave this page?"; }};

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