Clean • Professional
A generator is a special type of function that can pause and resume its execution.
function* syntax.yield to return values one at a time.Syntax :
function* generatorFunction() {
yield value1;
yield value2;
return finalValue; // optional
}
yield: Pauses the generator and returns a value.return: Ends the generator; value is returned and done becomes true.Basic Example
function* numbers() {
yield 1;
yield 2;
yield 3;
}
const gen = numbers();
console.log(gen.next()); // { value: 1, done: false }
console.log(gen.next()); // { value: 2, done: false }
console.log(gen.next()); // { value: 3, done: false }
console.log(gen.next()); // { value: undefined, done: true }
yield calls.You can iterate over a generator using:
a. for...of Loop
function* letters() {
yield 'A';
yield 'B';
yield 'C';
}
for (const letter of letters()) {
console.log(letter);
}
// Output: A B C
b. while Loop with .next()
const gen = letters();
let result = gen.next();
while (!result.done) {
console.log(result.value);
result = gen.next();
}
// Output: A B C
You can pass values back into a generator using .next(value):
function* counter() {
const start = yield "Enter start value:";
yield start + 1;
yield start + 2;
}
const gen = counter();
console.log(gen.next()); // { value: "Enter start value:", done: false }
console.log(gen.next(5)); // { value: 6, done: false }
console.log(gen.next()); // { value: 7, done: false }
Generators can handle errors using .throw():
function* genFunc() {
try {
yield 1;
} catch (err) {
console.log('Caught:', err);
}
}
const gen = genFunc();
console.log(gen.next()); // { value: 1, done: false }
gen.throw(new Error("Oops")); // Caught: Error: Oops
Generators are perfect for lazy sequences:
function* infiniteNumbers() {
let i = 0;
while (true) {
yield i++;
}
}
const gen = infiniteNumbers();
console.log(gen.next().value); // 0
console.log(gen.next().value); // 1
console.log(gen.next().value); // 2
async and await for advanced flow control.