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Promisification

Promises/Async/Await: Promisification

Can you explain what “promisification” is in JavaScript?​

View Answer:
Interview Response: “Promisification” is a long word for a simple transformation, and it is the conversion of a function that accepts a callback into a function that returns a promise. Such transformations are often required in real-life, as many functions and libraries are callback-based. But promises are more convenient, so it makes sense to “promisify” them.

Code Example:

let loadScriptPromise = function (src) {
  return new Promise((resolve, reject) => {
    loadScript(src, (err, script) => {
      if (err) reject(err);
      else resolve(script);
    });
  });
};

// usage:
// loadScriptPromise('path/script.js').then(...)

What is one crucial aspect to remember when using promisifications?​

View Answer:
Interview Response: Promisification is an excellent approach, especially when using async/await, but not a total replacement for callbacks. Remember, a promise may have only one result, but a callback may technically be called many times. So promisification is only meant for functions that call the callback once, and further calls get ignored.