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Serialize form data into a query string

Written byPhuoc Nguyen
17 Mar, 2020
Last updated
07 May, 2021
Level 1 — Basic
The following function serializes the form data which consists of names and values of its fields:
const serialize = function (formEle) {
// Get all fields
const fields = [].slice.call(formEle.elements, 0);

return fields
.map(function (ele) {
const name = ele.name;
const type = ele.type;

// We ignore
// - field that doesn't have a name
// - disabled field
// - `file` input
// - unselected checkbox/radio
if (!name || ele.disabled || type === 'file' || (/(checkbox|radio)/.test(type) && !ele.checked)) {
return '';

// Multiple select
if (type === 'select-multiple') {
return ele.options
.map(function (opt) {
return opt.selected ? `${encodeURIComponent(name)}=${encodeURIComponent(opt.value)}` : '';
.filter(function (item) {
return item;

return `${encodeURIComponent(name)}=${encodeURIComponent(ele.value)}`;
.filter(function (item) {
return item;
Note that we convert the collection of form elements to array by
const fields = [].slice.call(formEle.elements, 0);

See also

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