Test for front end engineers

I'm starting with a warm-up exercise.

Create a function to reverse a string

My answer

// reverse('Hello'); // olleH
const testString = "Hello";

function reverse(str) {
    const len = str.length;
    let newstr = "";

    for (let i = (len - 1); i >= 0; i--) {
        newstr += str[i];
    }
    return newstr;
}

reverse(testString);

Example answer

// reverse('Hello'); // olleH
const testString = "Hello";

function reverse(str) {
    return str.split("").reverse().join("");
}

reverse(testString);

Create a function that takes a string and returns a new string with duplicates removed.

My answer

const str = "This is is a test test string";

function removeDuplicates(val) {
	let isString = false;
	if (typeof val === "string") {
		val = val.split(" ");
		isString = true;
	}

	const breadcrumbs = {};
	const result = [];

	for (let i = 0; i < val.length; i++) {
		if (!breadcrumbs[val[i]]) {
			result.push(val[i]);
			breadcrumbs[val[i]] = true;
		}
	}
	return isString ? result.join(" ") : result;
}

console.log(removeDuplicates(str));

Example answer

const str = "This is is a test test string";

function removeDuplicates(str) {
  const arr = str.split(" ");

  const set = new Set(arr);
  const newString = [...set].join(" ");

  return newString;
}

console.log(removeDuplicates(str));

Without using .flat(), create a function to flatten an array

My answer

const arr = [1, 2, [3, 4, [5, 6, 7], 8], 9, 10];
const newarray = [];

function flatten(arr) {
  for (let i = 0; i < arr.length; i++) {
    if (!Array.isArray(arr[i])) {
      newarray.push(arr[i]);
    }
    else {
      flatten(arr[i]);
    }
  }
  return newarray;
}

console.log(flatten(arr));

Example answer

const arr = [1, 2, [3, 4, [5, 6, 7], 8], 9, 10];
const newarray = [];

function flatten(arr) {
  return arr.reduce((acc, item) => {
    if (Array.isArray(item)) {
      acc = [...acc, ...flatten(item)];
    }
    else {
      acc.push(item);
    }
    return acc;
  }, []);
}

console.log(flatten(arr));