yield and Generator Control Flow

In short: yield is a two-way channel, not just an exit. It sends a value out to whoever called .next() — but it's also an expression that pauses there, waiting to be given a value back. Whatever you pass into the following .next(v) call becomes that paused yield expression's own result. Beyond stepping through with .next(), two more methods control a generator from outside: .return(v) stops it early, and .throw(err) raises an error at the exact point it's paused, letting the generator's own try/catch handle it if it has one.

Pass answers back into a paused generator

The argument to .next(v) becomes the value of the yield expression that's currently paused — a real, two-way conversation:

it.next() (no argument) starts the generator and pauses at the first yield, returning { value: "What's your name?", done: false } — its argument is ignored, since there's no paused yield yet to receive it. it.next("Asha") supplies "Asha" as that paused yield's result, which is assigned to name, and the generator runs on to the next yield. it.next("great") finishes it the same way, returning { value: "Asha says: great", done: true } from the return statement.

Stop a generator early with return()

.return(v) ends the generator immediately, wherever it's currently paused — as if a return v; had been written right there:

After one yield, .return("stopped early") finishes the generator on the spot, returning { value: "stopped early", done: true } — "Red Dawn" and "Green Tide" are never reached. Any further .next() calls after that just return { value: undefined, done: true }, the same as a normally finished generator.

Raise an error inside a paused generator

.throw(err) makes the paused yield throw err, right there inside the generator — its own try/catch can catch it, exactly like a synchronous error:

After the first yield, .throw(new Error("skip track")) raises that error exactly where the generator is paused. Because that spot sits inside a try block, the generator's own catch handles it, logs the message, and yields "recovered" instead of the error propagating out to the caller.

Quick practice

🎯 Your turn

Trace function* chat() { const name = yield "What's your name?"; const mood = yield \Hi ${name}, how are you?`; return `${name} says: ${mood}`; } const it = chat(); it.next(); it.next("Asha"); it.next("great");and explain what eachnext()call returns, and specifically what value the firstyield` expression evaluates to and why.

Write your explanation and submit it — there's no code to run here, just your reasoning.