work of promise in javascript code example

Example 1: js create a promise

/*
	A Promise is a proxy for a value not necessarily known when the promise is created. 
    It allows you to associate handlers with an asynchronous action's eventual success 
    value or failure reason.
*/            
let promise = new Promise((resolve , reject) => {
  fetch("https://myAPI")
    .then((res) => {
      // successfully got data
      resolve(res);
    })
    .catch((err) => {
      // an error occured
      reject(err);
    });          
});

Example 2: what is a promise

// Promise is a special type of object that helps you work with asynchronous operations.
// Many functions will return a promise to you in situations where the value cannot be retrieved immediately.

const userCount = getUserCount();
console.log(userCount); // Promise {<pending>}

// In this case, getUserCount is the function that returns a Promise. If we try to immediately display the value of the userCount variable, we get something like Promise {<pending>}.
// This will happen because there is no data yet and we need to wait for it.

Example 3: making promises in js

getData()
    .then(data => console.log(data))
    .catch(error => console.log(error));

Example 4: javascript promises

var posts = [
  {name:"Mark42",message:"Nice to meet you"},
  {name:"Veronica",message:"I'm everywhere"}
];

function Create_Post(){
  setTimeout(() => {
    posts.forEach((item) => {
      console.log(`${item.name} --- ${item.message}`);
    });
  },1000);
}

function New_Post(add_new_data){
  return new Promise((resolve, reject) => {
    setTimeout(() => {
     posts.push(add_new_data);
      var error = false;
      if(error){
        reject("Something wrong in </>, Try setting me TRUE and check in console");
      }
      else{
        resolve();
      }
    },2000);
  })
}

New_Post({name:"War Machine",message:"I'm here to protect"})
    .then(Create_Post)
    .catch(err => console.log(err));