How hard can be this JavaScript Interview Question from UBER?

JavaScript Interview Question - 68 | In this video, we will see how to solve a medium-difficulty problem asked in a frontend engineer interview to SDE1, SDE2, and SDE3.

We have to implement a function named mapLimit in JavaScript that takes an array of async tasks (promises) and a callback function as input, executes a limited number of tasks in batches, and then after each promise is settled invokes the callback function with the result of passed and failed results.

You can expect this frontend system design/coding question in Rippling, Uber, Flipkart, Atlassian, Meta, Google, Microsoft, Dropbox, TCS, Infosys, Wipro, Cognizant, Capgemini, Accenture, Nvidia, Nutanix, and other product-based organizations' interviews.

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[sagarmusic]

A little bit longer but more understandable solution, also it aways give ordered output according on the input list

const chop = (input, limit) => {
let res = []
let i = 0
let k = 0
while (i < input.length) {
let temp = []
while (k < limit) {
if (i == input.length) {
break
}
temp.push(input[i])
k++
i++
}
res.push(temp)
k = 0
}
return res
}


function getNamebyId(id, callback) {
const rRt = Math.floor(Math.random() * 100) + 200;

setTimeout(() => {
callback('User' + id)
}, rRt)

}

const performOp = async (choppedInput, iterateeFn) => {

try {
let resultList = [];

for (let i = 0; i < choppedInput.length; i++) {
for (let j = 0; j < choppedInput[i].length; j++) {
const result = await new Promise((resolve) => {
iterateeFn(choppedInput[i][j], resolve);
});

resultList.push(result);
}
}

return resultList;
} catch (error) {
throw error;
}
}


async function mapLimit(inputs, limit, iterateeFn, callback) {
const choppedInput = chop(inputs, limit)
const res = await performOp(choppedInput, iterateeFn)
callback(res)
}

mapLimit([5, 3, 2, 4, 1], 2, getNamebyId, (allResults) => {
console.log("output", allResults)
})

[chandrasekharmandapalli]

I would like to take personal guidance from you prashanth bhai for FE-2 roles

[aakashsrivastava]

I think you shouldn't use any helper functions like reduce as they are not allowed in interviews most of the time.

[harishrm]

Greetings, I have seen you async sequence video where you finally mentioned sequence can be done in async await way also, if we could do the same for this problem it will avoid the complexity of reduce right, I tried but I'm lacking when again durning the async parallel inside that await part, do you have another video for during this with async await way please?

[justlifethings]

Why are you batching here ? Max limit of operations is 2 right. So if you are batching, you are waiting both 1 & 2 to be completed to run 3. 3 can be run right away when either 1 or 2 is completed right ?

[vijaynavale]

Hi Prashant nice video✓
When you saw this question first time did you able to solve it on your own ? Or Did you take any reference ?

[kotadiyachaitanya]

Bhaiya do you looking for video editor?

[aayushgupta]

Would following approach be acceptable? This works correctly.

class A{
constructor(numOfProcesses, cb, limit){
this.limit = limit;
this.waitingList = [];
this.size = 0;
this.numOfProcesses = numOfProcesses;
this.responses = [];
this.cb = cb;
}
subscribe(fn){
if(this.size===this.limit) this.waitingList.push(fn);
else{
this.size++;
this.execute(fn);
}
}
async execute(fn){
const res = await fn();
this.responses.push(res);

return
}else{
this.size--;
}
if(this.responses.length === this.numOfProcesses){
this.cb(this.responses);
}
}
};
async function getNameById(id){
const time = 3000
return new Promise(res => setTimeout(()=>{
return res(`User${id}`)
}, time))
}
function mapLimit(inputs, limit, iterateeFn, cb){
const obj = new A(inputs.length, cb, limit);
inputs.forEach((input)=>{
obj.subscribe(iterateeFn.bind(this, input))
})
}
mapLimit([1, 2, 3, 4, 5], 1, getNameById, (answer)=>{
console.log(answer)
})