Promise.all handle exceptions

demo.js

function fetchData(x) {
  return new Promise((resolve, reject) => {
    // mock
    if (x == 3 || x == 4 || x == 5) {
      reject('error');
    } else {
      resolve(x);
    }
  });
}

/**
 * render page with an array
 * @param {array} data
 */
function render(data) {
  // render logic ...
  console.log(data);
}

/**
 * TODO: implement this function
 * fetch multiply requests simultaneous, and render the page with response data array.
 * if more than 3 requests fails, don't do render.
 * @param {number} n
 */
function fetchAndRender(n) {
  const arr = [];
  for (let i = 0; i < n; i++) {
    arr.push(fetchData(i));
  }
  let count = 0;

  return Promise.all(
    arr.map(item => {
      return item.catch(err => {
        count++;
        return err;
      });
    })
  ).then(res => {
    if (count <= 3) {
      render(res.filter(item => item !== 'error'));
      return Promise.resolve();
    } else {
      return Promise.reject();
    }
  });
}

fetchAndRender(10)
  .then(() => {
    console.log('render success');
  })
  .catch(() => console.log('render failed'));