This concept is used to ensure that every callback function which is called returns some value. See the API reference here. For example, if Playing with the first example with and without limits, and seeing how it affects the duration when reading 20 files:// Promise.map awaits for returned promises as well.// Promise.map awaits for returned promises as well.// The return value of .map is a promise that is fulfilled with an array of the mapped values// That means we only get here after all the files have been statted and their contents read// into memory. Bluebird is a fully featured JavaScript promises library with unmatched performance. If you need to do more operations per file, they should be chained in the map For...Introduction to Node.js The modern web application has really come a long way over the years with...What is GraphQL? The modern web application has really come a long way over the years with the introduction of many...A module in Node.js is a logical encapsulation of code in a single unit. npm install bluebird. We will look at an example of how to use the bluebird module. Step 2) The next step is to include the bluebird module in your code and promisify the entire MongoDB module. So if a Node JS module contains a callback function which does not return a value, and if we Promisify the node module, all the function's in that specific node module would automatically be modified to ensure that it returns a value. If "then" connection is established, then it will get all of the records in the collection and display them in the console accordingly. Given a finite Iterable(arrays are Iterable), or a promise of an Iterable, which produces promises (or a mix of promises and values), iterate over all the values in the Iterable into an array and map the array to another using the given mapper function.. Bluebird is a fully featured JavaScript promises library with unmatched performance. The mapper function has signature (value, index, arrayLength) where value is the current element (or its resolved value if it is a promise). Our example will first establish a connection to the "Employee collection" in the "EmployeeDB" database.
Bluebird is a fully-featured Promise library for JavaScript. Bluebird is a fully featured promise library with focus on innovative features and performance. Code Explanation:-The require command is used to include the Bluebird library. To use Bluebird from within a Node application, the Bluebird module is required. The strongest feature of Bluebird is that it allows you to "promisify" other Node modules in order to use them asynchronously. By promisify, we mean that bluebird will ensure that each and every method defined in the MongoDB library returns a promise. See the bluebird website for further documentation, references and instructions. The mapper function for a given item is called as soon as possible, that is, when the promise for that item's index in the input array is fulfilled. To install the Bluebird module, run the below command If the above steps are carried out properly, all of the documents in the Employee collection will be displayed in the console as shown in the output below.
Promises in Node.js 10 are significantly faster than before. If an element is a promise, the iterator will wait for it before proceeding. Iterables with Promise.map, Promise.each, and Promise.filter. For bluebird 2.x documentation and files, see the 2.x tree. If you need to do more operations per file, they should be chained in the map// The return value of .map is a promise that is fulfilled with an array of the mapped values// That means we only get here after all the files have been statted and their contents read// into memory. This doesn't mean that the result array has items in random order, it means that The concurrency limit applies to Promises returned by the mapper function and it basically limits the number of Promises created. Note.