for Loops.js

// Courtesy of Kusu

/*
for (const value of obj) {
  // loop body
}
*/
{
  const it = obj[Symbol.iterator]();
  try {
    for (let step; step = it.next(), !step.done; ) {
      const value = step.value;
      // loop body
    }
  }
  catch(e) { throw e; }
  finally { it.return(); }
}

/*
for (const key in obj) {
  // loop body
}
*/
{
  let current = obj;
  do {
    const keys = Reflect.ownKeys(current);
    const keysLength = keys.length;
    for (let i = 0; i < keysLength; ++i) {
      const key = keys[i];
      if (!Object.getOwnPropertyDescriptor(current, key).enumerable) continue;
      // loop body
    }
    if (current === Object.prototype) break;
    current = Object.getPrototypeOf(current);
    if (current === null) break;
  } while(true);
}


// Courtesy of MrLeebo
/* <forEach vs. for of */

// for...of: control flow
for (const obj of arr) {
  if (obj.skip) continue;
  if (obj.terminate) break;
  return obj.name;
}

// no .forEach equivalent

 
// for...of: visible side effect
for (const obj of arr) {
  obj.sendEmailNotification();
}

const processObject = obj => obj.sendEmailNotification();

// forEach: side effect declaration and execution are separated
arr.forEach(processObject);
/* forEach vs. for of> */


// Expected async behaviour. One request after the other
for (const entity of entities) {
  await fetch(
    remote,
    {
      headers: {
        "Content-Type": "application/json; charset=utf-8",
      },
      body: JSON.stringify(entity),
    }
 );
}

// Spam requests!
entities.forEach(async (entity) => {
  await fetch(
    remote,
    {
      headers: {
        "Content-Type": "application/json; charset=utf-8",
      },
      body: JSON.stringify(entity),
    }
 );
});