fake fetch iife closure test

fake-fetch-iife.js

// 20 March 2024
// fake fetch iife closure test

// Twitter posed a question at
// https://twitter.com/jcubic/status/1770519375944040682

// So I answered. I've since been blocked. *shrug*

// Here's what I get with a fake fetch, F:

// An async function returns a resolved promise.

async function F(url) { return url; }

// The log function in the promise.then() clause will report the current
// value of `id`, not its value when the fake request is made.

for (var id of ['a', 'b', 'c']) {
  F('/path/' + id).then(value => console.log(value, id));
}

// In this case, all logs of `id` resolve to `c`, the final value at the
// end of the for loop.

/*
/path/a c
/path/b c
/path/c c
*/

// An IIFE for each loop step fixes that by capturing the value at
// request time in the function's parameter list:

for (var id of ['a', 'b', 'c']) {
  (function (id) {
    F('/path/' + id)
      .then(value => console.log(value, id));
  })(id);
}

/*
/path/a a
/path/b b
/path/c c
*/