Form Serialize

Before you can POST a form as JSON or drop it into state, you have to turn its scattered fields into one object. That sounds trivial until you hit the real rules: unchecked checkboxes vanish, a checkbox group becomes an array, a multi-select yields several values under one name, and names like user[address][city] are meant to build nested structure. This is exactly what jQuery.serializeObject, the qs library, and Rails' form params do.

Implement formSerialize(form) returning a nested object. Lean on FormData, which already knows which controls are "successful". See MDN: FormData.

Signature

function formSerialize(form) {
  // returns a plain (possibly nested) object
}

Examples

// <input name="user[name]" value="Ada">
// <input type="checkbox" name="tags[]" value="a" checked>
// <input type="checkbox" name="tags[]" value="b" checked>
formSerialize(form);
// { user: { name: 'Ada' }, tags: ['a', 'b'] }

// <input type="checkbox" name="agree">        (unchecked)
// <select name="colors" multiple> red*, blue* selected
formSerialize(form);
// { colors: ['red', 'blue'] }   — no `agree` key at all

Notes

• Successful controls only — unchecked checkboxes/radios and unselected options don't appear. new FormData(form) applies these rules for you.
• Bracket names build structure — user[addr][city] → { user: { addr: { city } } }; tags[] appends into an array.
• Repeats become arrays — a multi-select or a checkbox group (same plain name, or name[]) collects multiple values into one array.
• Values are strings — form control values are always strings; a checked checkbox with no value is 'on'.