Is '.then(function(a){ return a; })' Necessary in Promise Chains?

Chaining Promises: Understanding ".then(function(a){ return a; })"

When working with promise chains, it's common to encounter statements like ".then(function(a){ return a; })". This syntax appears in the code:

var getEvents = function(participantId) {  
  return new models.Participant()
    .query({where: {id: participantId}})
    .fetch({withRelated: ['events'], require: true})
    .then(function(model) {
      return model;
    });
};

The question arises: is this function functionally identical to returning fetch() directly, without the additional ".then()"?

The Answer: A No-Op

Yes. ".then(function(a){ return a; })" is effectively a no-operation (no-op) for promises. It returns the same promise, acts in the same manner, and can be called equivalently.

Reasoning:

Promises are used to represent asynchronous operations. When a promise is resolved, it passes its result to the next promise in the chain via the "then" function. However, when the "then" function simply returns the input, it does not add any value to the chain.

Why the Author Might Have Used It:

The inclusion of the seemingly redundant ".then()" may be attributed to one of two reasons:

• Blunder: It's possible that the author simply made a mistake or misunderstood the purpose of promises.
• Lack of Comprehension: The author might have mistakenly believed that every promise needed a "then" function, even if it didn't do anything.

Bottom Line:

In most cases, ".then(function(a){ return a; })" is unnecessary and can be omitted without affecting the desired behavior. It's a placeholder that serves no purpose and should be removed for better code clarity.

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