JavaScript

💥 Questions by roadmap.sh roadmap.sh is the 6th most starred project on GitHub and is visited by hundreds of thousands of developers every month.

❓ CHALLENGE

function recursiveMaxSubarraySum(nums, startIndex = 0, currentSum = 0, maxSum = -Infinity) {
  if (startIndex === nums.length) {
    return maxSum;
  }

  currentSum = Math.max(nums[startIndex], currentSum + nums[startIndex]);
  maxSum = Math.max(currentSum, maxSum);

  return recursiveMaxSubarraySum(nums, startIndex + 1, currentSum, maxSum);
}

const result = recursiveMaxSubarraySum([-2, 1, -3, 4, -1, 2, 1, -5, 4]);

console.log(result);

⭐️ Updates from the TC39 meeting in February 2024 Stage changes: - Several proposals advanced to stage 1. - Stage 2: “Promise.try” - Stage 3: “Uint8Array to/from base64 and hex” - Stage 4: “ArrayBuffer.prototype.transfer and friends” - Several proposals became inactive. New ECMAScript proposal stage: 2.7 🟨 “Stage 2.7 is equivalent to what we used to call Stage 3. It means that the design is considered complete, we have a full specification, and we need to write code (tests and non-polyfill implementations) to gain feedback and make progress. It’s a strong signal.” 🟨“Stage 3 has been strengthened and now also means that test262 conformance tests are ready. This is a useful signal to JS engines that a proposal is truly ready to be implemented.” 🟨“Why did we do this? We separated out the ‘Approved in Principle: Spec Ready’ stage from the later ‘Recommended for Implementation: Tests Ready’ stage to reduce wasted effort in writing tests before spec stability, whilst also clarifying the test readiness message to engines.” TC39 member Jordan Harband comments: “[Stage 2.7 is] explicitly without the signal that it’s safe to ship unflagged, or use in production (which includes publishing polyfills). Stage 3 remains the signal for these things.” ecmascript.new

❓ CHALLENGE

const numbers = [1, 2, 3, 4, 5];

const sum = numbers.reduce((acc, curr) => {
  setTimeout(() => {
    acc += curr;
  }, 0);
  return acc;
}, 0);

console.log(sum);

👀🔵 React.memo is great. but sometimes, you shouldn't use it Hovhannes

❓ CHALLENGE

function recursiveNQueens(n) {
  const board = Array.from({ length: n }, () => Array.from({ length: n }, () => "."));

  const solutions = [];

  const isSafe = (row, col) => {
    for (let i = 0; i < row; i++) {
      if (board[i][col] === "Q") return false;
      const colOffset = row - i;
      if (col - colOffset >= 0 && board[i][col - colOffset] === "Q") return false;
      if (col + colOffset < n && board[i][col + colOffset] === "Q") return false;
    }
    return true;
  };

  const placeQueens = (row) => {
    if (row === n) {
      solutions.push(board.map(row => row.join("")));
      return;
    }
    for (let col = 0; col < n; col++) {
      if (isSafe(row, col)) {
        board[row][col] = "Q";
        placeQueens(row + 1);
        board[row][col] = ".";
      }
    }
  };

  placeQueens(0);

  return solutions;
}

const result = recursiveNQueens(4);

console.log(result);

❓ CHALLENGE

function recursivePascalTriangle(n, row = [1], triangle = []) {
  triangle.push(row);
  if (n === triangle.length) {
    return triangle;
  }
  const nextRow = [1];
  for (let i = 1; i < row.length; i++) {
    nextRow.push(row[i] + row[i - 1]);
  }
  nextRow.push(1);
  return recursivePascalTriangle(n, nextRow, triangle);
}

const result = recursivePascalTriangle(5);

console.log(result);

❓ CHALLENGE

function* generatorQuiz() {
  yield 1;
}

const generator = generatorQuiz();

setTimeout(() => console.log(generator.next().value), 0);

for (const value of generator) {
  console.log(value);
}

👀 Take a Qwik Break from React with Astro Paul Scanlon compares React to Qwik using several examples and concludes that Qwik is at least worth exploring as a React alternative. PAUL SCANLON

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❓ CHALLENGE

const obj = {
  0: 'a',
  1: 'b',
  length: 2
};

const result = Array.from(obj);

console.log(result);