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@idibidiart
Forked from sebmarkbage/Infrastructure.js
Last active September 10, 2020 00:53
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SynchronousAsync.js
const fetch = (url) => {
return new Promise((resolve, reject) => {
setTimeout(() => {
console.log(url)
switch(url.match(/\d[aA-zZ]$/)[0]) {
case "1a":
resolve({name: "Seb"})
// or try this instead:
// reject({error: "something went wrong while fetching " + url})
break;
case "1b":
resolve({name: "Markbage"})
}
}, 1000)
})
}
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(
obj => {
pending.delete(url);
cache.set(url, obj);
},
error => {
pending.delete(url);
throw error
}
)
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 = fetchTextSync('/users/' + id)
return user.name;
}
function getGreeting(name) {
if (name === 'Seb Markbage') {
return 'Hey';
}
return 'Hello';
}
function getMessage() {
let firstName = getUserName('1a')
let lastName = getUserName('1b')
let name = firstName + ' ' + lastName
return getGreeting(name) + ', ' + name + '!';
}
runPureTask(getMessage).then(message => console.log(message), errMsg => console.log(errMsg.error));
@idibidiart
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idibidiart commented Dec 17, 2017

This is a fork of @sebmarkbage 's genius "Poor Man's Algebraic Effects"

I added promise rejection scenario (see "try this" comment) and composition of fetchTextSync:

I like how I can compose idiomatically with this, e.g.: let result = fetchSync('/test/1a') + ' ' + fetchSync('/test/1b')

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