Nested Promise chain

promise-chain.js

// the array to loop through
const arr = [0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16];

// start with a resolved promise
let p = Promise.resolve();

// loop through the array
for (let i of arr) {
  
  // create promise chain
  p = p.then(() => {
    
    // return the promise for chaining
    return functionWithPromise(i);
    
  });
  
}

// dummy function with promise
function functionWithPromise(text) {
  
  // return a promise
  return new Promise((resolve, reject) => {
    
    // start the function
    console.log(`start promise: ${text}`);
    
    // simulate asyncronous activity
    setTimeout(() => {
      
      // end the function
      console.log(`end promise: ${text}`);
      
      // resolve the promise
      resolve(text);
      
    }, 1000);
    
  });
  
}