let cache = new Map(); | |
let pending = new Map(); | |
function fetchTextSync(url) { | |
if (cache.has(url)) { | |
return cache.get(url); | |
} | |
if (pending.has(url)) { | |
throw pending.get(url); | |
} | |
let promise = fetch(url).then( | |
response => response.text() | |
).then( | |
text => { | |
pending.delete(url); | |
cache.set(url, text); | |
} | |
); | |
pending.set(url, promise); | |
throw promise; | |
} | |
async function runPureTask(task) { | |
for (;;) { | |
try { | |
return task(); | |
} catch (x) { | |
if (x instanceof Promise) { | |
await x; | |
} else { | |
throw x; | |
} | |
} | |
} | |
} |
function getUserName(id) { | |
var user = JSON.parse(fetchTextSync('/users/' + id)); | |
return user.name; | |
} | |
function getGreeting(name) { | |
if (name === 'Seb') { | |
return 'Hey'; | |
} | |
return fetchTextSync('/greeting'); | |
} | |
function getMessage() { | |
let name = getUserName(123); | |
return getGreeting(name) + ', ' + name + '!'; | |
} | |
runPureTask(getMessage).then(message => console.log(message)); |
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@jaredpalmer The point is not for the whole program and event loop to be synchronous. Just a small part of it. At some point you have to have a coordinator that says what happens to the rest of the program while you're blocked. Note that this is not throwing an This thing is very much optimizing for most things to not block on I/O and is cached. The major downside is not the throw, it is that you may have to reuse some work if it does. If you're expecting to mostly hit I/O in many places I'd recommend |
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I added promise rejection scenario (see "try this" comment) and composition of fetchTextSync: https://gist.github.com/idibidiart/69fd5f9df339b5ef1783e6a8fae9fa51 I like how I can compose idiomatically with this, e.g.: let result = fetchSync('/test/1a') + ' ' + fetchSync('/test/1b') |
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This is awesome. Couple of questions:
runPureTask()
on line 18 have.then
after it? Isn't the point to be able to call it all synchronously?