JavaScript syntax
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A generator function is signified placing an * after the keyword function and contains one or more yield statements. The effect is to return a value and pause execution at the current state. Declaring an generator function returns an iterator. Subsequent calls to iterator.next() resumes execution until the next yield. When the iterator returns without using a yield statement there are no more values and the done property of the iterator is set to true.cite-ref-21[21]
function* generator() {
yield "red";
yield "green";
yield "blue";
}
let iterator=generator();
let current;
while(current=iterator.next().value)
console.log(current); //displays red, green then blue
console.log(iterator.next().done) //displays true
Async/await
The await operator in JavaScript can only be used from inside an async function or at the top level of a module. If the parameter is a promise, execution of the async function will resume when the promise is resolved (unless the promise is rejected, in which case an error will be thrown that can be handled with normal JavaScript exception handling). If the parameter is not a promise, the parameter itself will be returned immediately.cite-ref-23[23]
Below is an example (modified from thiscite-ref-async-await-javascript-async-await-25-0[25] article):
async function createNewDoc() {
let response = await db.post({}); // post a new doc
return db.get(response.id); // find by id
}
async function main() {
try {
let doc = await createNewDoc();
console.log(doc);
} catch (err) {
console.log(err);
}
}
main();
Node.js
version 8 includes a utility that enables using the standard library callback-based methods as promises.
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