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formDataMap()

A function that behaves like the FormData DOM interface, but returns immediately useful values for each type of form control.

How it works

/*
For the given `form` element,
with an optional `submitter` element,
return an object whose keys
are the names of the form elements,
mapping to their corresponding values
based on the type of each element.
*/

function formDataMap(form, submitter) {

const excludedTags = ['FIELDSET', 'OBJECT', 'OUTPUT']
const excludedTypes = ['button', 'reset', 'image'];

function shouldSubmit(el) {
if (!el.name) return false;
if (excludedTags.includes(el.tagName)) return false;
if (excludedTypes.includes(el.type)) return false;
if (el.type === 'submit' && el !== submitter) return false;
if (el.type === 'radio' && !el.checked) return false;
if (el.type === 'checkbox' && !el.checked) return false;
if (el.disabled || el.matches(':disabled')) return false;
if (el.closest('datalist')) return false;
return true;
}

const result = {};

function append(key, val) {
result[key] =
Object.hasOwn(result, key) ?
[].concat(result[key], val)
: val;
};

Array.from(form.elements).forEach(el => {
if (!shouldSubmit(el)) return;
const { name, type } = el;
if (type === 'number' || type === 'range') {
append(name, +el.value);
} else if (type === 'date' || type === 'datetime-local') {
append(name, el.valueAsDate());
} else if (type === 'file') {
append(name, el.files);
} else if (type === 'url') {
append(name, new URL(el.value));
} else if (type === 'select-one' || type === 'select-multiple') {
el.selectedOptions.forEach(
option => append(name, option.value)
);
} else {
append(name, el.value);
}
});

return result;
};