promise dom functions code example

Example 1: promise js

A promise is an object that may produce a single value some time in the future: 
either a resolved value, or a reason that it’s not resolved

Example 2: promise js

//example
function tetheredGetNumber(resolve, reject) {
  try {
    setTimeout( 
      function() {
        const randomInt = Date.now();
        const value = randomInt % 10;
        try { 
          if(value >= THRESHOLD_A) {
            throw new Error(`Too large: ${value}`);
          } 
        } catch(msg) {
            reject(`Error in callback ${msg}`); 
        }
      resolve(value);
      return;
    }, 500);
  } catch(err) {
    reject(`Error during setup: ${err}`);
  }
  return;
}