Understanding the meaning of `.then()` in Excel JavaScript involves recognizing its function

    Excel.run(function (context) {
    var sheet = context.workbook.worksheets.getItem("Sample");
    var range = sheet.getRange("B2:C5");
    range.load("address");

    return context.sync()
        .then(function () {
            console.log(`The address of the range B2:C5 is "${range.address}"`);
        });
}).catch(errorHandlerFunction);

In the provided documentation, I have a good grasp on most of the code. However, there is one line that I find confusing.

  .then(function ()
  1. I have already researched related keywords online.
  2. I have also referred to this (website)
  3. While I am familiar with VBA, I am still learning javascript.
typescript

Answer №1

In the realm of APIs, like the Office API and many others, responses are often in the form of a Promise, which serves as a way to handle asynchronous operations. Promises come equipped with a then function that specifies what action to take when the Promise is resolved, meaning that the async task has been completed.

Promises serve as an alternative to traditional callback functions.

This explanation hopefully sheds some light on this concept.

Answer №2

One of the key concepts in Javascript is the Promise. To gain a better understanding of how promises work, take a look at these resources https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Promise

In essence, promises act as proxy objects that are returned in response to asynchronous calls. These objects do not have a set value when created. Instead, once the value is determined, it triggers the function specified in the .then handler.

A promise can exist in one of three states:

  1. Pending State -> signifies that it is merely a proxy object without any assigned value
  2. Fulfilled State -> indicates that there is a value ready for retrieval, which can be processed using the .then handler
  3. Rejected State -> suggests that an error has occurred and needs handling through the .catch method

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