How to serialize form data with vanilla JS

serialize.js

/*!
 * Serialize all form data into a query string
 * (c) 2018 Chris Ferdinandi, MIT License, https://gomakethings.com
 * @param  {Node}   form The form to serialize
 * @return {String}      The serialized form data
 */
var serialize = function (form) {

	// Setup our serialized data
	var serialized = [];

	// Loop through each field in the form
	for (var i = 0; i < form.elements.length; i++) {

		var field = form.elements[i];

		// Don't serialize fields without a name, submits, buttons, file and reset inputs, and disabled fields
		if (!field.name || field.disabled || field.type === 'file' || field.type === 'reset' || field.type === 'submit' || field.type === 'button') continue;

		// If a multi-select, get all selections
		if (field.type === 'select-multiple') {
			for (var n = 0; n < field.options.length; n++) {
				if (!field.options[n].selected) continue;
				serialized.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.options[n].value));
			}
		}

		// Convert field data to a query string
		else if ((field.type !== 'checkbox' && field.type !== 'radio') || field.checked) {
			serialized.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
		}
	}

	return serialized.join('&');

};