JavaScript Generator Communication

Written by Swapnil RajaPublished 24 Aug 2026

Values can be sent into a running generator through next, not just read out of it.

A yield expression itself has a value, supplied by the next next() call.

This turns a generator into a genuine two-way conversation.

Example

javascript

function* greeter() {
  const name = yield "What is your name?";
  yield "Hello " + name;
}

const g = greeter();

console.log(g.next().value);
console.log(g.next("Ada").value);

PreviousJavaScript Generator Functions NextJavaScript Custom Iterables

Example

javascript

function* demo() {
  try {
    yield 1;
    yield 2;
  } catch (error) {
    yield "caught: " + error.message;
  }
}

const g = demo();

g.next();

console.log(g.throw(new Error("stop")).value);

Example

javascript

function* forever() {
  let n = 0;
  while (true) {
    yield n;
    n++;
  }
}

const g = forever();

console.log(g.next().value);
console.log(g.next().value);
console.log(g.next().value);

Complete Example

html

<!DOCTYPE html>
<html>
<head>
  <title>JavaScript Generator Communication</title>
</head>
<body>

  <h1>Generator Communication</h1>

  <p id="out"></p>

  <script>
    function* adder() {
      let total = 0;
      while (true) {
        total += yield total;
      }
    }

    const g = adder();
    g.next();

    const after5 = g.next(5).value;
    const after10 = g.next(10).value;

    document.getElementById("out").textContent =
      "After adding 5: " + after5 + ", after adding 10 more: " + after10;
  </script>

</body>
</html>

JavaScript Generator Communication

Example

Passing Values In

Syntax

The First next Only Starts It

Example

A Running Total

Example

Ending Early with return

Example

Throwing Into a Generator

Example

An Infinite Loop Is Safe Here

Example

Complete Example

Try It Yourself

Important Points

Conclusion