Promise

A Promise in JavaScript is an object that represents the future result of an asynchronous operation, like fetching data, waiting for a timer, or reading a file.

It can be in one of three states: pending, fulfilled, or rejected.

• new Promise(...) creates a new promise

• res means resolve, rej means reject

• rej() makes the promise fail

• .then() runs only when the promise is fulfilled

• .catch() runs when the promise is rejected

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• Analysis() represents an analysis operation that takes 3 seconds. After the analysis finishes, res() tells JavaScript: "The work is completed successfully."

• This waits for 3000 milliseconds = 3 seconds.

Reference

• https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Using_promises...