String

Per-instance text holder: stores one string locally, with a Length output and optional latch-until-Set behaviour.

String holds a single text value that belongs to this node instance alone — it is not named or shared (for an app-wide named value use Variable2). The value input sets it and savedValue (Value) reads it back; length always reports the stored string's character count. While the saveValue (Set) signal input is unconnected, values written to value apply immediately; once saveValue is connected the node latches: incoming values are held pending and only applied when Set fires — the idiomatic way to snapshot a text field at the moment of a click. Incoming values are cast with JavaScript String(). changed fires only when the stored value actually changes; stored fires after every Set trigger.

When to use it

Use it to hold or snapshot local text: capture a Text Input's current value on submit, keep a reusable literal in one editable place, or derive length for validation. For text shared across components use Variable2 + Set Variable; for computed text use an Expression.

At a glance


Category	Variables
Type name	`String`
Available in	browser, cloud
SSR compatibility	safe
Provided by	`noodl-runtime`
Behaviour spec	version 2 (under the hood)

Inputs

Values

Name	Type	Default	Description
`runOnChange-value`	Boolean	`true`	Whether a new value on Value re-runs this node. On by default; untick to make this input passive so only the control signal runs it
`treatEmptyAs`	Enum (`null`, `empty-string`)	`null`	Back-compat for graphs written before Variables were nullable. `null` (default) keeps a cleared value distinguishable from a real "". Choosing another option restores the pre-NDA-003 coercion for authors who relied on it.
`treatUnchangedAs`	Enum (`unchanged`, `done`)	`unchanged`	What this node reports when the action was valid and there was nothing to do. Unchanged (the default) keeps it a third outcome of its own. Done suits a project whose chains should carry on either way. Completed fires whatever this is set to.
`value`	String	``	The empty-value contract (dev-docs/reference/EMPTY-VALUE-CONTRACT.md): `undefined` abstains and leaves the Variable's stored value untouched. `null` is a real value — it clears the Variable, is stored, and fires Changed. What "cleared" is stored as is controlled by `Treat empty as` (null by default).

Signals

Name	Type	Default	Description
`saveValue`	Signal	—	Stores the latest value now. This is additional to Value storing on change; untick Value under Run On Value Change to stop that

What each input does

Value (value)

undefined: ignored → Changed stays silent
the same as the last one, or Run On Value Change unticked: held for the next Set → Changed stays silent
a new value that converts to what is already stored: held, nothing changes → Changed stays silent
a new value, with Run On Value Change ticked: stored straight away (an empty one as Treat Empty As says) → Changed

Set (saveValue)

always: at the end of the frame the last Value is stored — Changed and Done if that changed it, otherwise Unchanged (or what Treat Unchanged As says)

Outputs

Values

Name	Type	Default	Description
`length`	Number	—	0 when the Variable is cleared (`savedValue` is `null`) — there is no text to measure, and 0 is what an author reading this as a plain number expects, rather than a thrown error or `null` itself.
`savedValue`	String	—	Can be `null` — a cleared Variable (see `value`'s description) stores and emits null by default, not this type's zero value, unless `Treat empty as` says otherwise.

Signals

Name	Type	Default	Description
`changed`	Signal	—	Fires whenever the stored value actually changed, however it was reached — including Value writing straight through under Run On Value Change. It is a value-level event, not the outcome of a Set
`completed`	Signal	—	Fires after every invocation, whatever the outcome — wire this to carry on regardless. Failure still fires and still carries its reason, so this cannot hide an error
`done`	Signal	—	Fires when a Set stored a value the Variable was not already holding
`unchanged`	Signal	—	Fires when a Set stored the value it already held, so nothing changed. ⚠️ With Value left ticked under Run On Value Change this is the common case, because Value has already stored by the time Set fires

Patterns

Snapshot on submit: Text Input onTextChanged → value, Button onClick → saveValue; stored then triggers whatever consumes the committed text.
length → an Expression or Condition for 'minimum characters' style validation.

Watch out for

Using String nodes in two components to 'share' text — each instance has its own value. Use Variable2 for shared text.

Examples

Share a value between components with Set Variable and Variable

The idiomatic shared-state shape, contrasting per-instance and app-wide storage. In the form component, a String node snapshots the text field: because its saveValue (Set) is connected, keystrokes only latch a pending value, and the Button click commits it. The String's stored signal then fires the Set Variable's do, writing the committed text into the app-wide variable 'userName' (setWith 'string' types the dynamic value input). In a completely separate component, a Variable2 node bound to the same name reads the value reactively — its changed/value update the greeting automatically whenever the variable is written, with no connection between the two components.

Boolean, Number, Color, Variable, Set Variable, Expression, Text Input

Code export

Exports to React. A project that uses it exports this node as React code.

How export works shows what an export writes, with a worked example.

Under the hood

This node's behaviour is written down as an executable spec in @nodegx/node-spec, version 2. The spec is the reference the conformance tests grade the runtime against. Every rule in it cites the line of the runtime it was read from. The full spec is at the bottom of this page.

What it depends on outside the node

Nothing. Its outputs depend only on its inputs and its own state.

Starting state

{
  "current": "",
  "hasBeenSet": false,
  "sets": 0
}

How inputs are converted

Inputs not listed arrive as sent.

Input	Conversion	What it does
Value (`runOnChange-value`)	`not-false`	only an explicit `false` turns it off; no value, `0` and `""` leave it on

How actions report back

Each time Set is triggered, the node reports exactly one of Done or Unchanged.

The code it replaces

What you would write by hand instead:

a string held in state, set from elsewhere: const [name, setName] = useState('')

The full spec

The spec's source, as the docs were generated. Helpers it imports live beside it in packages/nodegx-node-spec/src.

packages/nodegx-node-spec/src/nodes/string.ts
/**
 * String — read from `packages/noodl-runtime/src/nodes/std-library/variables/string.ts` on
 * 2026-09-30 (NSP-011). The family's rules are in variable-base.ts; this file is what string.ts
 * supplies, plus the one output the family does not have: `length` (:37-59).
 */

import { defineNode } from '../spec';
import { afterSets, CHANGED, onSet, onValue, SAVED_VALUE_DESCRIPTION, VARIABLE_OUTCOMES, variableInputs, variableState, type VariableArgs } from './variable-base';

/** :12-35 — startValue '' (:15); `cast` is `String(value)` (:25-27); empty options null / '' (:31-34) */
export const STRING: VariableArgs & { type: 'string' } = {
  type: 'string',
  startValue: '',
  cast: (value) => String(value),
  emptyOptions: [
    { value: 'null', label: 'Null (default)', coerce: null },
    { value: 'empty-string', label: 'Empty string ("")', coerce: '' }
  ]
};

export const StringVariable = defineNode({
  type: 'String',
  // v2 (P109 ISL-027, row C5 ruled "Start with no remembered value"): a first Value of 0 is stored and fires
  // Changed like any other value, and a Set before any Value reports Unchanged. v1 ignored a first 0 (it equalled
  // a hidden seed of 0) and a Set before any Value stored that seed and reported Done.
  version: 2,
  source: 'packages/noodl-runtime/src/nodes/std-library/variables/string.ts',
  // NSP-018 — the hand-written code this node replaces (read by nothing yet; `spec-ledger` counts it)
  idioms: [
    { says: 'a string held in state, set from elsewhere', example: 'const [name, setName] = useState(\'\')' }
  ],
  state: variableState(STRING),
  inspect: (s) => String(s.current),
  outcomes: VARIABLE_OUTCOMES,
  inputs: variableInputs(STRING),
  outputs: {
    savedValue: { type: 'string', from: (s) => s.current, displayName: 'Value', group: 'Values', description: SAVED_VALUE_DESCRIPTION },
    // :40-58 — `typeof value === 'string' ? value.length : 0`; flagged on every changed store (:28-30)
    length: {
      type: 'number',
      from: (s) => (typeof s.current === 'string' ? s.current.length : 0),
      displayName: 'Length',
      group: 'Values',
      description:
        '0 when the Variable is cleared (`savedValue` is `null`) — there is no text to ' +
        'measure, and 0 is what an author reading this as a plain number expects, rather than ' +
        'a thrown error or `null` itself.'
    },
    changed: CHANGED
  }
}).on(
  { value: (s, v, i) => onValue(STRING, s, v, i), saveValue: onSet },
  { afterInputs: (s, i) => afterSets(STRING, s, i) }
);

Generated

This page is generated from node-catalog-enriched.json, the node's spec in packages/nodegx-node-spec and the export ledger. Do not edit it by hand — run npm run docs:nodes to regenerate, and fix the source instead.

When to use it​

At a glance​

Inputs​

Values​

Signals​

What each input does​

Outputs​

Values​

Signals​

Patterns​

Watch out for​

Examples​

Related nodes​

Code export​

Under the hood​

What it depends on outside the node​

Starting state​

How inputs are converted​

How actions report back​

The code it replaces​

The full spec​

When to use it

At a glance

Inputs

Values

Signals

What each input does

Outputs

Values

Signals

Patterns

Watch out for

Examples

Related nodes

Code export

Under the hood

What it depends on outside the node

Starting state

How inputs are converted

How actions report back

The code it replaces

The full spec