chain-promise's Introduction

chain-promise

Simple implementation for chaining promises !!

Install

npm install chain-promise

Example

Let suppose we have 3 Async Process like this

var asyncProcess1 = function (obj) {
  return new Promise(function (resolve) {
    setTimeout(function () {
      console.log("inside asyncProcess1", obj);
      obj.a = "a";
      resolve(obj);
    }, 2000);
  })
};
var asyncProcess2 = function (obj) {
  return new Promise(function (resolve) {
    setTimeout(function () {
      console.log("inside asyncProcess2", obj);
      obj.b = obj.a + "b";
      resolve(obj);
    }, 2000);
  })
};
var asyncProcess3 = function (obj) {
  return new Promise(function (resolve) {
    setTimeout(function () {
      console.log("inside asyncProcess3", obj);
      obj.c = obj.b + "c";
      resolve(obj);
    }, 2000);
  })
};

And, We want to execute these Promises one by one. We want to pass data from one to another.

This is simple task, can be done like this.

var D1 = {};
asyncProcess1(D1).then(function (D2) {
  asyncProcess2(D2).then(function (D3) {
    asyncProcess3(D3).then(function (D4) {
      console.log("Final data is, ", D4);
    });
  });
});

You can see, we are passing data from each async process to another by one by one.

This works, But there are two problems

This kind of chain and passing data from one another can be automated !
If there are dynamic list of asyncProcessors then above solution will not work.

For this reason, I have created this tiny library.

Above functionality can be re-written as

var chainPromise = require("chain-promise");
chainPromise([asyncProcess1, asyncProcess2, asyncProcess3], D1).then(function (D4) {
  console.log("Final data is, ", D4);
});

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