Cards and Buttons can have a JavaScript function.


Function Argument (Payload)

When does it execute?

Return Value

Technical Details

Both timeout after 8 seconds. If you open a File that has a Card Code error, you'll see a spinner until it times out. Similarly, if the execution on a Button fails, and the Button has more actions, they'll execute after the timeout.

For security, functions run inside Web Workers. Therefore, there are limitations. For example, no direct DOM manipulation.


This example has Keys (they're explained in the next section, but take a look at them here first).

Key Editor showing set keys

CardCode. The JavaScript editor pre-populates a snippet that sums numeric Entries that have Keys. In this example:

function (card) {
  const side_a = card.byKey.side_a.value;
  const side_b = card.byKey.side_b.value;
  return side_a + side_b;

After hitting Apply, the Total will be computed by that function. And it will recompute when the Entries change.

Key Editor

Keys are for referencing specific Cards or Entries in the payload. They don't have to be unique. If repeated, the last one wins.

ViewKey Editor

Suggests Keys based on the Card Title or Entry Label.

Key Editor showing suggestions

With the Keys set.

Key Editor with accepted keys

Key Grammar

Case-sensitive and must begin with a letter. Then, they can have underscores and digits.

name   last_name   LastName2  
_name   1name


The payload, the argument to be passed to the function, describes the Card and its children. Each child is a description of either an Entry, or a Nested Card.

If you want Entries or Totals from other Cards, connect them to the Card with the code. By the way, those connected targets can be Hidden in Previewer.

As hidable children show up in the payload, you can use them for API keys, tokens, etc.

Like in Formulas, Nested Cards get computed first. Therefore, their Totals are ready to use in the parent payload (asynchronous code is supported).

Tip There's a Download Payload Mock button that shows the exact argument your function will be called with.

Card (Root or Nested)

  • key String
  • value Card Total as a Number
  • stringValue Card Total as a String
  • children Array, in order, of the Entries and Nested Cards
  • byKey Object literal to reference children directly (unordered)
  • isNumeric Boolean, true if the Card has a numeric Total. As Totals can only be numeric, this is like a hasTotal. But as Entries also have an isNumeric property, this consistent naming is handy for cases like the Max example below


  • key String
  • value Number if it's numeric; 1 or 0 if it's a Checkbox; String otherwise
  • stringValue
  • struck Boolean for Strikethrough
  • label String
  • isNumeric Boolean


Sum All

function (card) {
  return card.children
    .reduce((sumSoFar = 0, child) => sumSoFar + child.value);

That function is like Formula PresetsSum All, but the actual preset does more checks, see the next example.


Equivalent to Formula PresetsMaximum.

Ensures computing on numeric children that aren't struck. And handles when there are none by returning an empty string.

Although Nested Cards have no struck property, it's safe to filter it.

function (card) {
  const values = card.children
    .filter(child => child.isNumeric && !child.struck)
    .map(child => child.value);

  return values.length
    ? Math.max(...values)
    : '';

Count children costing 50 or more

function (card) {
  return card.children
    .filter(child => child.value >= 50)

Sum children costing over 50

function (card) {
  return card.children
    .filter(child => child.value > 50)
    .reduce((sumSoFar = 0, child) => sumSoFar + child.value);


The price gets a 15% discount if buying 10 or more, or 25% on 50+.

Two cards setup two compute a discounted price

The Auxiliary Card code:

function (card) {
  const num_of_bags = card.byKey.num_of_bags.value;
  const base_price  = card.byKey.base_price.value;
  const discounts   = card.byKey.volume_discounts.children;

  let discountSoFar = 0;
  for (const step of discounts)
    if (num_of_bags >= Number(step.label))
      discountSoFar = step.value;

  return base_price * (1 - discountSoFar);

Examples with HTTP Requests

This zip has the server-side handlers for these examples.


Card with an Auxiliary Entry for passing a parameter to a remote API for setting its Card Total with the response
function (card) {
  const product_id = card.byKey.product_id.value;
  return fetch(`http://localhost:7000/in-stock-count/${product_id}`)
    .then(response => response.json())
    .then(data => data.count)


Card with an Auxiliary Entry for passing a parameter to a remote API for use as API key. And two other Entries the sides of a triangle for computing its hypotenuse in a server side API.
function (card) {
  return fetch('http://localhost:7000/hypotenuse', {
    body: JSON.stringify(card),
    method: 'POST',
    headers: new Headers({ 'Content-Type': 'application/json' })
    .then(response => response.json())
    .then(data => data.hypotenuse)

HTTP Post Button

A Card with a Button with a JavaScript action
function (card) {
  return fetch('http://localhost:7000/form-submit', {
    body: JSON.stringify(card),
    method: 'POST',
    headers: new Headers({ 'Content-Type': 'application/json' })
    .then(() => '')
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