node js promise example

Example 1: javascript promise

var promise = new Promise(function(resolve, reject) {
  // do some long running async thing…
  
  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }
  else {
    reject(Error("It broke"));
  }
});

//usage
promise.then(
  function(result) { /* handle a successful result */ },
  function(error) { /* handle an error */ }
);

Example 2: promise js

We use promise to make a  AsyncFunction, cose simetime we have to wait that function give 
us some result.
Example, if we use ajax we have await ajax data or statament.
_____________________________________
Make a simple example.
_____________________________________
var asyncronus_function= (number)=>
		{
			return new Promise( (accept, reject)=>
			{
			})
		}                 
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this function return a promise Object, thet required a function executor
this functions (accept, reject) are defined in the executor 
function, that was needed in promise constructor.
Syntax: new Promise (executor)
executor= (accept, reject) =>{}

if function end well we return a accept(), otherwise reject()
_____________________________________
Let complete asyncronus_function
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var asyncronus_function= (number)=>
		{
			return new Promise( (accept, reject)=>
			{
				if(number>10)
				return accept("my first async");
				return reject("my first async error")
			})

		}
if it dont return any of this 2 function, Promise state is [PENDING] ,
if return accept is [RESOLVED]  end if return reject is [REJECTED]
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how we can retrieve accept or reject?
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there is two methods really important, that we have to consider afther we call this function
1) .then(function(error){}) is call when promise state is [RESOLVED]
2) .error(function(error){}) is call when promise state is [REJECTED]
3) do nothing if [PENDING]
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let call asyncronus_function()!!! 
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	asyncronus_function(MY_NUMBER).then(function(data)
        {
			console.log(data)
    	}).catch(error => 
        {
      			console.log(error)
    	});
		
if  MY_NUMBER> 10 ,asyncronus_function print data : OUTPUT my first async
if MY_NUMBER<10 , asyncronus_function print error : OUTPUT my first async error
HOPE it halp and have a nice day!

Example 3: formidable nodejs example

// make this a middleware function, 
// then put it on the route like you used jwt,
// then get the value with req.users.

const { IncomingForm } = require('formidable')
const { resolve } = require('path')
const { existsSync, writeFileSync } = require('fs')

module.exports = (req, res, next) => {
  const form = new IncomingForm({
    maxFileSize: 1 * 1024 * 1024,
    keepExtensions: true
  })

  form.parse(req, (error, fields, file) => {
    if (error) return next(error)
    const patternFile = /\.(jpg|jpeg|png|svg|gif|raw|webp)$/gi.test(file.productImage.name)

    if (patternFile) {
      const pathFile = resolve(process.cwd(), 'servers/uploads/', file.productImage.name)
      const fileExits = existsSync(pathFile)
      if (!fileExits) {
        writeFileSync(pathFile)
        req.users = JSON.parse(JSON.stringify({ fields, file }))
        return next()
      }
      req.users = JSON.parse(JSON.stringify({ fields, file }))
      return next()
    }
  })
}

Example 4: js promise examples

//Promise to load a file...
//use with openFile(url, fCallback);
//fCallback(fileContents){ //do something with fileContents}
const loadFile = url => {
    return new Promise(function(resolve, reject) {
        //Open a new XHR
        var request = new XMLHttpRequest();
        request.open('GET', url);
        // When the request loads, check whether it was successful
        request.onload = function() {
            if (request.status === 200) {
                // If successful, resolve the promise
                resolve(request.response);
            } else {
                // Otherwise, reject the promise
                reject(Error('An error occurred while loading image. error code:' + request.statusText));
            }
        };
        request.send();
    });
};
const openFile = (url, processor) => {
    loadFile(url).then(function(result) {
            processor(result);
        },
        function(err) {
            console.log(err);
        });
};

Example 5: nodejs promise then example

p.then(onFulfilled, onRejected);

p.then(function(value) {
   //  run
  }, function(reason) {
  // fail
});

Example 6: .promise()

var promise = new Promise(function(resolve, reject) {
  // do some long running async thing…
  
  if (/* everything turned out fine */) {
    resolve("Stuff worked!");
  }
  else {
    reject(Error("It broke"));
  }
});