Promises & Iteration

Promises, generators, async functions, and the iteration protocol are not available in SSJS. The SFMC server-side JavaScript engine (Jint) implements an ES3/ES5-era dialect, predates ES2015, and executes synchronously — there is no event loop or microtask queue. Promise, Iterator, Generator, GeneratorFunction, and every async variant are undefined, and new Promise(...) throws Unknown type: Promise.

Status legend

Icon	Meaning
❌ Missing	Not available (`typeof` is `"undefined"`; construction throws)

Members

Member	ES	Status	Notes
`Promise`	ES6	❌ Missing	Engine is synchronous — no `.then`/`await`
`Iterator`	ES6	❌ Missing	No iteration protocol; use index loops
`Generator`	ES6	❌ Missing	`function*` syntax is not supported
`GeneratorFunction`	ES6	❌ Missing	—
`AsyncFunction`	ES2017	❌ Missing	`async`/`await` unsupported
`AsyncGenerator`	ES2018	❌ Missing	—
`AsyncGeneratorFunction`	ES2018	❌ Missing	—
`AsyncIterator`	ES2018	❌ Missing	—

Promise

(ES6) — ❌ Missing. Promise is not defined — typeof Promise === "undefined" and new Promise(function(resolve){ resolve(1); }) throws Unknown type: Promise.

The SSJS engine runs synchronously, so asynchronous flow control is neither needed nor available. All Platform and HTTP calls are blocking — write straight-line code and read return values directly:

// No Promise/await — HTTP calls return synchronously.
var resp = HTTP.Get("https://postman-echo.com/get");
Write(resp.StatusCode);   // available immediately

Iterator

(ES6) — ❌ Missing. Iterator is not defined. Because Symbol is also absent, there are no well-known symbols and therefore no iterator protocol — for…of, spread, and destructuring over iterables are unavailable. Iterate arrays with a classic index loop:

for (var i = 0; i < arr.length; i++) {
    Write(arr[i] + "\n");
}

Generator

(ES6) — ❌ Missing. Generator is not defined, and the function* / yield generator syntax is not supported by the engine’s parser. Return a fully-materialised array instead of yielding lazily.

GeneratorFunction

(ES6) — ❌ Missing. GeneratorFunction (the hidden constructor of generator functions) is not defined.

Async variants

(ES2017+) — ❌ Missing. AsyncFunction, AsyncGenerator, AsyncGeneratorFunction, and AsyncIterator are all not defined. The async / await keywords are not supported. Since the engine is synchronous, model any “async” work as ordinary blocking calls.