# gt-node: General Translation Node.js SDK: declareVar
URL: https://generaltranslation.com/en-GB/docs/node/reference/functions/declare-var.mdx
Docs index: https://generaltranslation.com/llms.txt
Description: Mark a value as non-derivable within a General Translation derive call. API reference for declareVar.

A non-derivable value is one that the General Translation compiler cannot statically analyse. Use `declareVar` inside a [`derive`](/docs/node/reference/functions/derive) call to isolate the part of an expression that must be treated as a runtime variable.

## Overview [#overview]

Call `declareVar` with a value to get back an encoded ICU `select` string that carries the value as its `other` branch. This lets the compiler keep the surrounding content derivable while treating the wrapped value as a variable.

```ts
import { declareVar, derive, getGT } from 'gt-node';

const gt = await getGT();
const message = gt(`My name is ${derive(declareVar(getName()))}`);
```

Signature:

```ts
declareVar(
  variable: string | number | boolean | null | undefined,
  options?: { $name?: string }
): string
```

## How it works [#how-it-works]

* **Non-derivable marker.** `declareVar` wraps its argument in an ICU `select` expression (`{_gt_, select, other {...}}`) so the compiler treats it as a variable rather than a static value.
* **Optional name.** Pass `$name` to label the variable in the encoded output.
* **Recovery.** Decode a string containing `declareVar` output back to its interpolated form with [`decodeVars`](/docs/node/reference/functions/decode-vars).

## Parameters [#parameters]

| Parameter               | Description                         | Type                                               | Optional | Default |
| ----------------------- | ----------------------------------- | -------------------------------------------------- | -------- | ------- |
| [`variable`](#variable) | The value to mark as non-derivable. | `string \| number \| boolean \| null \| undefined` | No       | —       |
| [`options`](#options)   | Options for the declaration.        | `{ $name?: string }`                               | Yes      | —       |

### `variable` [#variable]

**Type** `string | number | boolean | null | undefined` · **Required**

The value to mark as non-derivable. It is coerced to a string and sanitised.

### `options` [#options]

**Type** `{ $name?: string }` · **Optional**

* `$name?: string` — an optional name for the variable, included in the encoded output.

## Returns [#returns]

**Type** `string`

An encoded ICU `select` string carrying the value (and optional name).

## Examples [#examples]

```ts
import { declareVar, derive, getGT } from 'gt-node';

function derivableName() {
  if (someCondition) {
    return declareVar(Math.random().toString());
  }
  return 'John Doe';
}

const gt = await getGT();
const greeting = gt(`My name is ${derive(derivableName())}`);
```

## Notes [#notes]

* Use `declareVar` only inside a [`derive`](/docs/node/reference/functions/derive) call.
* Decode encoded variables back to text with [`decodeVars`](/docs/node/reference/functions/decode-vars).

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