lazy-promise.js

function query(label) {
  console.log(`(${label}) created 'lazy promise', but not started yet`);
  return {
    then(r) {
      console.log(`(${label}) started!`);
      // ... process query
      // "return" them:
      r([{ data: `result for ${label}` }]);
    },
  };
}

// won't execute, it's lazy:
query(1);
console.log();

// will execute:
const results = await query(2);
console.log("(2) got results:", results);
console.log();

// will also execute:
query(3).then((results) => {
  console.log("(3) got results:", results);
});


// program output:
//
// (1) created 'lazy promise', but not started yet
//
// (2) created 'lazy promise', but not started yet
// (2) started!
// (2) got results: [ { data: 'result for 2' } ]
//
// (3) created 'lazy promise', but not started yet
// (3) started!
// (3) got results: [ { data: 'result for 3' } ]