# Build steps as a task list

> Run a list of async steps under a task list that animates on a terminal, prints each step once as it settles in CI, and stops at the first failure.

Source: https://flagstaff.interlace.tools/docs/recipes/build-steps

A build script runs steps in order and should say which one failed. On a terminal the list is
drawn with the running step animated; in CI each step is one line, written when it finishes.

```js title="steps.mjs"
import { setTimeout as sleep } from 'node:timers/promises';

import { hoist } from 'flagstaff/loop';
import { tasks } from 'flagstaff/tasks';

import { json, rt } from './rt.mjs';

const steps = [
  { title: 'install', run: () => sleep(100) },
  { title: 'build', run: () => sleep(100) },
  { title: 'test', run: () => Promise.reject(new Error('2 failing')) },
  { title: 'publish', run: () => sleep(100) },
];

const list = steps.map(({ title }) => ({ title, status: 'pending' }));
const flag = hoist(tasks(), rt, { tasks: list }, { json });

for (const [i, step] of steps.entries()) {
  list[i] = { title: step.title, status: 'running' };
  flag.update({ tasks: [...list] });
  try {
    await step.run();
    list[i] = { title: step.title, status: 'ok' };
  } catch (error) {
    list[i] = { title: step.title, status: 'fail', detail: error.message };
    process.exitCode = 1;
    break;
  }
}
flag.lower({ tasks: [...list] });
```

```text title="node steps.mjs" exit="1"
✔ install
✔ build
✖ test
```

`publish` never ran and never settled, so nothing is printed for it. Pass a new array to each
`update()` rather than mutating the one you hoisted with: the loop compares text, and a list you
changed in place is the list it already printed.

The script sets exit code 1, as a failing build should. Under `--json` an agent gets every transition, pending and running
included, with the error message in `detail`.