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Frontend interview - Questions I was asked

Rajesh Royal on May 10, 2021

These are the questions I was asked In a frontend interview for a ReactJS position. If you ask me to clone Netflix UI I will do It in shortest p...
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faiwer profile image
Stepan Zubashev • 
result.reduce((acc, item) => acc + item.x, 0)

people.reduce((acc, item) => {
  if (item.gender === 'male') acc.male.push(item);
  else acc.female.push(item);
  return acc;
}, { male: [], female: [] });

eval(value.split('=')[0])
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diogo405 profile image
Diogo Goncalves •

people.reduce(...) answer is a masterpiece 👏🏻

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Rajesh Royal • • Edited

Masterpiece.

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Alejandra Monroy • • Edited 
const sortBy = (arr, attribute) => {
  const set = new Set();
  arr.map((element) => set.add(element[attribute]));

  const sorted = {};

  set.forEach(
    (setElement) => (sorted[setElement] = arr.filter((element) => element[attribute] === setElement))
    .forEach(element => delete element[attribute]),
  );

  return sorted;
};
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Antonijo Galic •

Using .filter for the second task

const output = () => {
  const male = people.filter(person => person.gender === 'male');
  const female = people.filter(person => person.gender === 'female');

  return { male: male, female: female };
};

output();
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Truong Phan •

A more generic solution to group by any property:

Array.prototype.groupBy = function (p) {
    return this.reduce((g, i) => {
        g[i[p]] = g[i[p]] || [];
        g[i[p]].push(i);
        return g;
    }, {});
};
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Rajesh Royal •

Didn't understand It can you explain a little more.

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infantiablue profile image
Truong Phan • • Edited

I may use the implicit variables so that you could read easily, see my comments for the explanations

// get the input property to group by, we attach the function to the prototype object
Array.prototype.groupBy = function (prop) {
    // then apply reduce
    return this.reduce((group, item) => {
        // create new property for the group object if not existed, if yes, reassign from the accumulator 
        group[item[prop]] = group[item[prop]] || [];
        // add new item to the group of property (in this  case, a list) we want to group
        group[item[prop]].push(item);
        return group;
   // create initial empty object to implement reduce
    }, {});
};
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Then we can use people.groupBy('gender') or people.groupBy('age')

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Saurav Behera •

people = [
// { name: 'Alice', age: 21, gender: "female" },
// { name: 'Max', age: 20, gender: "male" },
// { name: 'Jane', age: 20, gender: "female" },
// { name: 'Jon', age: 21, gender: "male" },
// { name: 'Alex', age: 20, gender: "male" }
// ]
// const male=people.filter((el)=>el.gender=="male")
// const female=people.filter((el)=>el.gender=="female")
// console.log({male:male,female:female})

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Saurav Behera •

// let result = [{x: 1}, {x: 2}, {x: 3}];
// res=result.reduce((acc,el)=>acc+el.x,0)

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Saurav Behera •

let value = "5+8=x";
let arr=value.split("=")
arr=arr[0].split("+").map(Number).reduce((acc,e)=>acc+e)
console.log(arr)