Editing Lazy evaluation (section)

====JavaScript====
In [[JavaScript]], lazy evaluation can be simulated by using a [[Generator (computer programming)|generator]]. For example, the [[Stream (computing)|stream]] of all [[Fibonacci numbers]] can be written, using [[memoization]], as:
<syntaxhighlight lang="js">
/**
 * Generator functions return generator objects, which reify lazy evaluation.
 * @return {!Generator<bigint>} A non-null generator of integers.
 */
function* fibonacciNumbers() {
    let memo = [1n, -1n]; // create the initial state (e.g. a vector of "negafibonacci" numbers)
    while (true) { // repeat indefinitely
        memo = [memo[0] + memo[1], memo[0]]; // update the state on each evaluation
        yield memo[0]; // yield the next value and suspend execution until resumed
    }
}

let stream = fibonacciNumbers(); // create a lazy evaluated stream of numbers
let first10 = Array.from(new Array(10), () => stream.next().value); // evaluate only the first 10 numbers
console.log(first10); // the output is [0n, 1n, 1n, 2n, 3n, 5n, 8n, 13n, 21n, 34n]
</syntaxhighlight>