TypeScript Form Serializer

Serializer.ts

/*
 * Serialize all form data into a query string (TypeScript version)
 * Based on the Chris Fernandi function.
 * 2020 Williams Crazut, MIT License, https://webdeveloperguy.com
 */
function serialize(form: HTMLFormElement)
{
    let serialized = [];

    for (let i = 0; i < form.elements.length; i++) {

        let field = form.elements[i] as HTMLInputElement | HTMLSelectElement;

        if (!field.name
            || field.disabled
            || field.type === 'file'
            || field.type === 'reset'
            || field.type === 'submit'
            || field.type === 'button'
        ) continue;
        
        if (field instanceof HTMLSelectElement) {
            if (field.type === 'select-multiple') {
                for (let n = 0; n < field.options.length; n++) {
                    if (!field.options[n].selected) continue;
                    serialized.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.options[n].value));
                }
            } else {
                serialized.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
            }
        }

        if (field instanceof HTMLInputElement) {
            if (field.checked) {
                serialized.push(encodeURIComponent(field.name) + "=" + encodeURIComponent(field.value));
            }
        }
    }

    return serialized.join('&');
}