I am trying to figure out a way to write below code using functional programming.
let member_found = [];
// going through 50 or more pagination until 5 are found.
while(member_found.length < 5)
{
let member = findMember(/* calls selenium commands to visit next page */);
if(member != undefined)
member_found.push(member);
}
console.log(member_found) // expecting 5 values but actual is 0.
currently, the code goes into infinite loop due to non-blocking nature of js.
you can wrap findMember to return a promise and than you can use ES6 async\await capabilities :)
lets say you have findMember(cb)
so it will be
function promiseFindMember() {
return new Promise((res, rej) => findMember(member => res(member)))
}
in this way you will be able to write your function as following
function async foo() {
let members = []
while(member_found > 5) {
let member = await promiseFindMember()
if(member !== undefined) {
members.push(member)
}
}
}
I also added an example to catch the concept and to compare between the ideas :)
function dummyCb(cb){
console.log("Dummy run!")
setTimeout(cb, 1000)
}
function promiseDummyCb(){
return new Promise((res, rej) => dummyCb(() => res()))
}
async function async_hello() {
cb_count = 0
while(cb_count < 5) {
await promiseDummyCb()
cb_count += 1
}
}
async function hello() {
cb_count = 0
while(cb_count < 5) {
dummyCb()
cb_count += 1
}
}
hello()At first ensure that findMember always returns something by retrying:
const find = cb => findMember(res => res ? cb(res) : find(cb));
Now to get an array of a certain length from a callback function we could do the same thing:
const fromAsync = (fn, length, cb, arr = []) => arr.length >= length
? cb(arr)
: fn(res => fromAsync(fn, length, cb, arr.concat(res)));
So you can finally do:
fromAsync(find, 10, result => {
console.log(result);
});
PS: there is definitely an easier way of doing this, but you wanted a functional approach...
findMemberan async function or doesit take a callback?let member = findMember(he's maybe just missing an await, otherwise that's not an async method..to visit next pageora lot of selenium callsorcalls selenium commandsis absolutely nothing to do with logic and very unclear context. Perhaps webpage stuff? If you comment to the code. Better not to use words of unclear context.findMemberIt's aweful manner not to speficy the key function.pseudo codedoes not mean to cut the core information. You add unnessary keywrords - pagenation, lots of calls, selnium command, but the most important information is hidden. Rewrite the code.