What approach can be taken to optimize this promise error handling?

One common approach is to have a fallback solution in place. If the primary element fails to render, then it attempts rendering with alternative renderers. How can this be refactored for optimal performance?

The issues with the current code are:

  • Renderers should be organized in an array, but they are currently structured within 'then' blocks.
  • If the initial renderer fails, it should fallback to another renderer for successful rendering.
  • The first renderer has a similar algorithm as the 2nd and subsequent renderers. This leads to duplication. However, the first one needs to run before the others, which can run concurrently and stop when any of them returns a result.
let first = $('#id1');

return this.render('priorityRenderer', first).then(isEmpty => {

  let els = [
    $('#id2'), $('#id3')
  ];

  if (isEmpty) {
    // move the initial element back to the pool for re-rendering below
    els.unshift(first);
  }

  return Promise.all(els.map(el => {
    return this.render('secondaryRenderer', el)
      .then(result => {
        if (result) {
          return result;
        } else {
          return this.render('3thRenderer', el)
        }
      })
      .then(result => {
        if (result) {
          return result;
        } else {
          return this.render('4thRenderer', el)
        }
      })
      .then(result => {
        if (result) {
          return result;
        } else {
          return this.render('5thRenderer', el)
        }
      });
    })
});

Answer №1

If you want to implement a method that calls a chain of renderers until the first one returns a result, you can follow one of these approaches:

renderers(rs, el, i=0) {
    if (i < rs.length)
        return this.render(rs[i], el).then(result => result || this.renderers(rs, el, i+1));
    else
        return Promise.reject(new Error("no renderer worked, tried: "+rs));
}

To use this method in your code, you can do the following:

let first = $('#id1');
let els = [$('#id2'), $('#id3')];
let rs = ['secondaryRenderer', '3rdRenderer', '4thRenderer', '5thRenderer'];

return Promise.all([
    this.renderers(['priorityRenderer'].concat(rs), first)
].concat(els.map(el =>
    this.renderers(rs, el)
)));

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