[Canonical page](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/evaluating-alternatives/>)
[Full documentation index](<https://docs.dhtmlx.com/planning-engine/llms.txt>)


# Evaluating Alternatives

This guide shows how to compare several possible edits in one raw `evaluate` call and pick the best one, for example to decide which resource should take a task. It covers building candidates, scoring them with and without leveling, reading the metrics, handling candidates that fail, keeping long evaluations off the main thread and committing the winner.

## How evaluation works

[`evaluate(candidates_json, options_json)`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>) is a method of a solved [`JsonProject`](<https://docs.dhtmlx.com/planning-engine/wasm/api/json-project.md>). `candidates_json` is a JSON array of [**candidates**](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md#candidate>). Each candidate is an object with an `id` and a `changes` field. `changes` holds a [`SchedulingChanges`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/scheduling-changes.md>) payload, the same JSON you'd pass to [`apply`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-apply.md>). One candidate is one alternative: "give task B to dev2", "split the review between two people", "add a link". The call scores every candidate against the project's accepted baseline and returns the scores in an envelope. The project isn't modified: `evaluate` is read-only, like [`preview`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-preview.md>).

Every candidate goes through the same run on a disposable copy of the project:

1. Copy the reference state. That's the accepted baseline, or its cleared copy with `clearFirst` (see [Options](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/evaluating-alternatives.md#options>)).
2. `apply` the candidate's changes.
3. [`solve`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-solve.md>) without data and measure the **scheduled** stage.
4. When the options set `level`, run [`level`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-level.md>) with those options and measure the **leveled** stage.

You'd run the same sequence to commit the candidate for real. Each candidate starts from the reference state, never from the previous candidate. Both stages are compared with the one baseline.

The [`result`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md#evaluateresult>) of the envelope has three fields:

- `baseline`: the metrics of the reference state itself. All its deltas are 0.
- `candidates`: one [entry](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md#candidateresult>) per candidate, in input order. An entry holds the candidate's `id`, `scheduled` metrics, `leveled` metrics (only with `level`) and a `cost`. A failed candidate has an `error` instead.
- `baselineId`: the token of the accepted baseline the candidates were scored against.

Each stage is described by a [`Metrics`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md>) object: the project finish and the finish of each focus task, resource overload, conflicts, cycles and a single `cost` number. Every measurement is an absolute `value` plus a `delta` against the baseline, so you can show either one.

Errors come in two levels. Problems with the call itself return an error envelope:

- no solved baseline: `kind: "project"`, `code: "no-baseline"`. This includes a project that had an `apply` since its last `solve`.
- a stale `baselineId` in the options or in any candidate's `changes`: `kind: "project"`, `code: "stale-baseline"`.
- an unknown focus task, leveling options that don't fit the baseline, or `level: true`: `kind: "validation"`.
- malformed JSON or an unknown field in a candidate or in the options: `kind: "parse"`.

Everything else fails only its own candidate. The candidate gets an `error` and no metrics, and the other candidates are scored as usual. See [Error handling](<https://docs.dhtmlx.com/planning-engine/wasm/error-handling.md>) for the envelope itself.

`evaluate` reports scores, not dates. The result has no task updates and no overallocation windows. Once you've picked a candidate, commit it with `apply` and `level`, or look at its dates with `preview`.

## Candidates

All examples on this page use the same small project: tasks A and B, two working days each, both starting on Monday, August 10, 2026, and both assigned to `dev1`. The resource `dev2` is idle, so `dev1` is overloaded for two days.

Build each alternative as a candidate object and pass the array to [`evaluate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>). An empty change set (`{}`) is a useful candidate too: it scores "leave the plan as it is" next to the other options.

```js
const { JsonProject } = require("./pkg-node/plen_wasm.js");

function unwrap(text) {
  const response = JSON.parse(text);
  if (!response.ok) {
    const { kind, code, message, path } = response.error;
    throw new Error(`${kind} ${code ?? ""}: ${message} (at ${path})`);
  }
  return response.result;
}

// Tasks A and B, two working days each, both on dev1 in the same week.
const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};

const candidates = [
  // Keep the plan as it is.
  { id: "stay", changes: {} },
  // Give task B to dev2.
  { id: "dev2", changes: { assignments: { update: [{ id: "aB", resource: "dev2" }] } } },
];

const project = new JsonProject("{}");
try {
  unwrap(project.solve(JSON.stringify(data), "{}"));

  const options = { focus: ["B"] };
  const result = unwrap(project.evaluate(JSON.stringify(candidates), JSON.stringify(options)));

  console.log(`baseline: cost ${result.baseline.cost}`);
  for (const candidate of result.candidates) {
    console.log(`${candidate.id}: cost ${candidate.cost}`);
  }
} finally {
  project.free();
}
```

```text
baseline: cost 2
stay: cost 2
dev2: cost 0
```

Without leveling, only the scheduled stage is scored. `stay` keeps both tasks on `dev1` and costs 2, two resource-days of overload. `dev2` removes the overload and costs 0.

The candidate `id` is echoed back so you can match results to inputs. Ids aren't checked for uniqueness, and results keep input order anyway. A candidate object takes only `id` and `changes`; any other field fails the whole call with a `parse` error. See the [`evaluate` reference](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>).

## Options

The [options object](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md#evaluateoptions>) has four fields, all optional:

- `level`: a [`LevelingOptions`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/leveling-options.md>) object levels each candidate after scheduling it and adds the leveled stage. `{}` uses the default leveling options. `false` or `null` (the default) scores the scheduled stage only. `true` isn't accepted: it returns a `validation` error.
- `focus`: one task id or an array of ids. These are the tasks to report finish dates and focus overload for. There's no implicit "modified task", so list the tasks your candidates are about.
- `baselineId`: a baseline token. The call fails with `stale-baseline` when it no longer names the accepted baseline. Each candidate's `changes.baselineId` is checked the same way.
- `clearFirst`: score against a copy with the in-scope `leveling_delay` and `pauses` cleared.

Leveling changes the picture. Without it, an overloaded plan looks bad on overload. With it, the overload turns into delay, which is what the user gets after committing and leveling:

```js
const { JsonProject } = require("./pkg-node/plen_wasm.js");

function unwrap(text) {
  const response = JSON.parse(text);
  if (!response.ok) {
    const { kind, code, message, path } = response.error;
    throw new Error(`${kind} ${code ?? ""}: ${message} (at ${path})`);
  }
  return response.result;
}

// Tasks A and B, two working days each, both on dev1 in the same week.
const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};

const candidates = [
  { id: "stay", changes: {} },
  { id: "dev2", changes: { assignments: { update: [{ id: "aB", resource: "dev2" }] } } },
];

const project = new JsonProject("{}");
try {
  unwrap(project.solve(JSON.stringify(data), "{}"));

  // `level: {}` levels each candidate with the default leveling options.
  const options = { level: {}, focus: ["A", "B"] };
  const result = unwrap(project.evaluate(JSON.stringify(candidates), JSON.stringify(options)));

  for (const candidate of result.candidates) {
    const leveled = candidate.leveled;
    if (!leveled) continue;
    const finish = leveled.finish.project;
    console.log(`${candidate.id}: project ends ${finish.date} (+${finish.delta} days), cost ${candidate.cost}`);
    for (const task of leveled.finish.tasks) {
      if (task.finish) console.log(`  ${task.id} ends ${task.finish.date} (+${task.finish.delta})`);
    }
  }
} finally {
  project.free();
}
```

```text
stay: project ends 2026-08-14 08:00 (+2 days), cost 2
  A ends 2026-08-12 08:00 (+0)
  B ends 2026-08-14 08:00 (+2)
dev2: project ends 2026-08-12 08:00 (+0 days), cost 0
  A ends 2026-08-12 08:00 (+0)
  B ends 2026-08-12 08:00 (+0)
```

For `stay`, leveling resolves the overload by pushing B two days later, so the cost is now the delay. For `dev2` there's nothing to level.

`level` runs with the options exactly as you pass them. Its own `clearFirst` defaults to `true`, so each candidate is re-leveled from zero. That creates a trap after an earlier `level` run. The stored delays are already in the baseline finish, and they hide the overload the current assignments cause. A candidate that removes the overload then shows a negative finish delta, because leveling from zero drops the old delays.

The top-level `clearFirst` in the evaluate options fixes this. It replaces the reference state with a copy that has the in-scope delays and pauses cleared, solved again. The baseline metrics and every candidate run then use that copy. The scope is `level.scope.tasks` when you give it, otherwise every task. It's independent of `level.clearFirst`, so it also works without `level`.

```js
const { JsonProject } = require("./pkg-node/plen_wasm.js");

function unwrap(text) {
  const response = JSON.parse(text);
  if (!response.ok) {
    const { kind, code, message, path } = response.error;
    throw new Error(`${kind} ${code ?? ""}: ${message} (at ${path})`);
  }
  return response.result;
}

// Tasks A and B, two working days each, both on dev1 in the same week.
const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};

const candidates = [
  { id: "dev2", changes: { assignments: { update: [{ id: "aB", resource: "dev2" }] } } },
];

const project = new JsonProject("{}");
try {
  unwrap(project.solve(JSON.stringify(data), "{}"));
  // The plan was leveled earlier: B carries a two-day leveling delay.
  const leveled = unwrap(project.level("{}"));

  const options = { baselineId: leveled.baselineId, level: {}, clearFirst: true };
  const result = unwrap(project.evaluate(JSON.stringify(candidates), JSON.stringify(options)));

  // The cleared baseline shows the overload that B's delay was hiding.
  console.log(`baseline overload: ${result.baseline.overload.total.value}`);
  for (const candidate of result.candidates) {
    const finish = candidate.leveled?.finish.project;
    if (finish) console.log(`${candidate.id}: finish delta ${finish.delta}`);
  }
} finally {
  project.free();
}
```

```text
baseline overload: 2
dev2: finish delta 0
```

With `clearFirst`, the baseline reports 2 resource-days of overload and the `dev2` candidate a finish delta of 0. Without it, the baseline has no overload and the same candidate shows a finish delta of -2. Both views are valid. Use `clearFirst` when you'll commit with `level` and its default `clearFirst: true`, which re-levels from zero.

A few details:

- `baselineId`, candidate tokens, `level` options and focus ids are all checked against the accepted state before anything is cleared. `clearFirst` adds no new errors.
- A candidate's own `changes.baselineId` is dropped before its trial run, because the cleared copy has a different token. The result's `baselineId` is still the accepted state's.
- When there's nothing to clear in scope, the output is the same as with `clearFirst: false`.

The full option list is on the [`evaluate` reference](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>). For the leveling options themselves, see [Leveling resources](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/leveling-resources.md>).

## Metrics and cost

Every stage reports the same [`Metrics`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md>) fields:

| Field | What it measures |
|---|---|
| `finish.project` | Latest end over scheduled tasks. `null` when the stage has no tasks. |
| `finish.tasks` | One `{ id, finish }` entry per focus task, in focus order. |
| `overload.total` | Overload over all resources. |
| `overload.resources` | Overload per resource, for every resource that's non-zero in the stage or the baseline. |
| `overload.focus` | Per focus task: the overload per resource in the buckets that intersect the task. |
| `conflicts`, `cycles` | How many conflicts and cycles the stage has. |
| `cost` | One number for ranking, lower is better. |

Dates come as a [**shift**](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md#shift>): `{ date, delta }`. `delta` is the working time from the baseline finish in `config.duration_unit`, positive when later. A task's delta is measured on its own calendar, the project's on the global calendar. `date` is a `YYYY-MM-DD HH:mm` string, like every date on the raw surface (see [Wire format](<https://docs.dhtmlx.com/planning-engine/wasm/wire-format.md>)). Counts and overload come as an [**amount**](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md#amount>): `{ value, delta }`.

Overload is measured the same way the leveler sees it. For each time bucket, it's how far a resource's load goes over its capacity, summed over buckets. The unit is capacity × buckets, so on a day basis `2` means "two resource-days over". One bucket size (basis) applies to the baseline and every stage of every candidate: `level.basis` when you give it, otherwise the one derived from `config.duration_unit`. [`loadProfile`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-load-profile.md>) shows the same per-resource sum as excess at that basis.

Focus overload shows where the trouble is. At the scheduled stage it's the overload around the task. At the leveled stage it's what leveling couldn't resolve there. A milestone has zero length and covers no bucket.

The leveled stage ([`LeveledMetrics`](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md#leveledmetrics>)) carries the same fields, flattened into one object, plus `converged`, `rounds` and `windows`. `windows` is the number of overallocation windows left after leveling.

`cost` is one fixed heuristic:

```text
cost = max(0, finish.project.delta)
     + overload.total.value
     + 1000 × (conflicts.value + cycles.value)
```

When the basis follows `duration_unit`, a day of delay and a resource-day of overload weigh the same. An earlier finish doesn't earn a bonus. The 1000 penalty keeps any broken schedule, with conflicts or cycles, behind every valid one. The candidate's own `cost` is the cost of the last stage present: leveled when you level, scheduled otherwise. The baseline carries its own `cost`.

If the heuristic doesn't fit your product, rank on the raw values instead. This function prints the per-resource overload change of each candidate's scheduled stage, given the parsed `result` of an `evaluate` envelope:

```js
function printOverload(result) {
  for (const candidate of result.candidates) {
    if (!candidate.scheduled) continue;
    for (const row of candidate.scheduled.overload.resources) {
      const { value, delta } = row.overload;
      console.log(`${candidate.id}: ${row.resource} overload ${value} (${delta} vs baseline)`);
    }
  }
}
```

For the project above, the `dev2` candidate prints `dev2: dev1 overload 0 (-2 vs baseline)`. The row for `dev1` is there because `dev1` was overloaded in the baseline, even though it's zero in the stage. Resources come in stage order, then resources that exist only in the baseline. See the [`Metrics` reference](<https://docs.dhtmlx.com/planning-engine/wasm/api/types/metrics.md>).

## Failed and cyclic candidates

A candidate can fail without failing the call. Three cases need handling:

- **Rejected.** [`apply`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-apply.md>) rejects an operation in the change set (the result reports only the first rejection), or `solve` or `level` fails on the candidate's input, for example on a leveling scope id the candidate removed. The entry has `error: { path, message }` and no `scheduled`, `leveled` or `cost`.
- **Cyclic.** The candidate creates a dependency cycle. `scheduled` is measured on the unchanged dates the cyclic solve returns, and `cycles.value` is above 0. Leveling stops at round 0 on a cyclic plan, so `leveled` is absent. The cycle penalty pushes the cost over 1000.
- **Focus task removed.** When the candidate removes a focus task, that task's `finish` and its focus overload `resources` are `null`. The rest of the metrics are normal.

```js
const { JsonProject } = require("./pkg-node/plen_wasm.js");

function unwrap(text) {
  const response = JSON.parse(text);
  if (!response.ok) {
    const { kind, code, message, path } = response.error;
    throw new Error(`${kind} ${code ?? ""}: ${message} (at ${path})`);
  }
  return response.result;
}

// Tasks A and B, two working days each, both on dev1 in the same week.
const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};

const candidates = [
  // Refers to an assignment that doesn't exist.
  { id: "missing", changes: { assignments: { update: [{ id: "nope", resource: "dev2" }] } } },
  // Links A and B both ways.
  {
    id: "cycle",
    changes: {
      links: {
        add: [
          { id: "ab", source: "A", target: "B", type: "fs" },
          { id: "ba", source: "B", target: "A", type: "fs" },
        ],
      },
    },
  },
  // Removes the focus task.
  { id: "removed", changes: { tasks: { remove: ["B"] } } },
];

const project = new JsonProject("{}");
try {
  unwrap(project.solve(JSON.stringify(data), "{}"));

  const options = { level: {}, focus: ["B"] };
  const result = unwrap(project.evaluate(JSON.stringify(candidates), JSON.stringify(options)));

  for (const candidate of result.candidates) {
    if (candidate.error) {
      console.log(`${candidate.id} rejected at ${candidate.error.path}: ${candidate.error.message}`);
      continue;
    }
    const scheduled = candidate.scheduled;
    if (scheduled.cycles.value > 0) {
      console.log(`${candidate.id} is cyclic, leveled: ${candidate.leveled !== undefined}`);
    }
    for (const task of scheduled.finish.tasks) {
      if (task.finish === null) console.log(`${candidate.id} removes focus task ${task.id}`);
    }
    console.log(`${candidate.id} cost ${candidate.cost}`);
  }
} finally {
  project.free();
}
```

```text
missing rejected at assignments.update[0]: unknown assignment id
cycle is cyclic, leveled: false
cycle cost 1002
removed removes focus task B
removed cost 0
```

The rejected entry in the envelope looks like this:

```json
{
  "id": "missing",
  "error": { "path": "assignments.update[0]", "message": "unknown assignment id" }
}
```

Rank only candidates that have a `cost`. The cyclic candidate has one, but the penalty keeps it at the bottom. Its 1002 is the cycle penalty plus the two resource-days of overload `dev1` still has.

Call-level errors still come back as an error envelope with `ok: false`, and no candidate is scored. For example, focusing on a task the project doesn't have:

```js
const response = JSON.parse(project.evaluate("[]", JSON.stringify({ focus: ["X"] })));
```

```json
{
  "ok": false,
  "error": { "kind": "validation", "code": null, "message": "unknown task \"X\"", "path": "focus[0]" }
}
```

A stale token returns `kind: "project"` with `code: "stale-baseline"`. See [Error handling](<https://docs.dhtmlx.com/planning-engine/wasm/error-handling.md>).

## Sequential only

Each candidate runs on its own copy, so candidates are independent of each other. The WebAssembly build still scores them one at a time, in input order, on the thread that calls [`evaluate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>).

:::note
Candidates are scored one after another.
:::

`evaluate` is synchronous and CPU-bound, like every raw export. A large evaluation blocks the calling thread until it returns. Keep it off the UI thread or the request loop by running it in a Web Worker or a Node.js worker thread. Each worker loads its own module instance and holds its own [`JsonProject`](<https://docs.dhtmlx.com/planning-engine/wasm/api/json-project.md>):

```js
// evaluate-worker.js
const { parentPort } = require("node:worker_threads");
const { JsonProject } = require("./pkg-node/plen_wasm.js");

// Each message carries the project data, the candidates and the options as JSON text.
parentPort.on("message", ({ dataJson, candidatesJson, optionsJson }) => {
  const project = new JsonProject("{}");
  try {
    const solved = project.solve(dataJson, "{}");
    // Reply with the solve error envelope, or with the evaluate envelope.
    parentPort.postMessage(JSON.parse(solved).ok ? project.evaluate(candidatesJson, optionsJson) : solved);
  } finally {
    project.free();
  }
});
```

```js
// main.js
const path = require("node:path");
const { Worker } = require("node:worker_threads");

const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};
// One candidate per resource that could take task B.
const candidates = ["dev1", "dev2"].map((dev) => ({
  id: dev,
  changes: { assignments: { update: [{ id: "aB", resource: dev }] } },
}));

const worker = new Worker(path.join(__dirname, "evaluate-worker.js"));
worker.once("message", (text) => {
  const response = JSON.parse(text);
  if (response.ok) {
    for (const candidate of response.result.candidates) {
      console.log(`${candidate.id}: cost ${candidate.cost}`);
    }
  } else {
    console.error(response.error);
  }
  worker.terminate();
});
worker.postMessage({
  dataJson: JSON.stringify(data),
  candidatesJson: JSON.stringify(candidates),
  optionsJson: "{}",
});
```

The worker prints `dev1: cost 2` and `dev2: cost 0`. Only JSON text crosses between the threads, so the envelope can go back unparsed. For the worker setup in the browser build, see [Run in a worker](<https://docs.dhtmlx.com/planning-engine/wasm/how-to/run-in-a-worker.md>).

## Committing the winner

[`evaluate`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-evaluate.md>) never changes the project. To commit the chosen candidate, run its changes for real: [`apply`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-apply.md>) the same change set, then [`level`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-level.md>) with the same leveling options, `step` included. With other options, the committed plan isn't the one that was scored. If you scored without `level`, follow `apply` with [`solve(undefined, …)`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-solve.md>) instead.

```js
const { JsonProject } = require("./pkg-node/plen_wasm.js");

function unwrap(text) {
  const response = JSON.parse(text);
  if (!response.ok) {
    const { kind, code, message, path } = response.error;
    throw new Error(`${kind} ${code ?? ""}: ${message} (at ${path})`);
  }
  return response.result;
}

// Tasks A and B, two working days each, both on dev1 in the same week.
const data = {
  tasks: [
    { id: "A", start_date: "2026-08-10 08:00", duration: 2 },
    { id: "B", start_date: "2026-08-10 08:00", duration: 2 },
  ],
  resources: [{ id: "dev1" }, { id: "dev2" }],
  assignments: [
    { id: "aA", task: "A", resource: "dev1", value: 1 },
    { id: "aB", task: "B", resource: "dev1", value: 1 },
  ],
};

const candidates = [
  { id: "stay", changes: {} },
  { id: "dev2", changes: { assignments: { update: [{ id: "aB", resource: "dev2" }] } } },
];

const project = new JsonProject("{}");
try {
  unwrap(project.solve(JSON.stringify(data), "{}"));

  const leveling = {};
  const options = { level: leveling };
  const result = unwrap(project.evaluate(JSON.stringify(candidates), JSON.stringify(options)));

  // Lowest cost wins; rejected candidates have no cost.
  let best = null;
  result.candidates.forEach((scored, i) => {
    if (scored.cost === undefined) return;
    if (best === null || scored.cost < best.cost) best = { cost: scored.cost, candidate: candidates[i] };
  });

  if (best) {
    // apply fails with stale-baseline if the project changed since the evaluation.
    const changes = { ...best.candidate.changes, baselineId: result.baselineId };
    const report = unwrap(project.apply(JSON.stringify(changes)));
    if (report.rejected.length === 0) {
      // The same options that scored the candidate.
      unwrap(project.level(JSON.stringify(leveling)));
      console.log(`committed ${best.candidate.id} (cost ${best.cost})`);
    }
  }
} finally {
  project.free();
}
```

```text
committed dev2 (cost 0)
```

Results come back in input order, so the index of a scored entry is the index of its candidate. Setting `baselineId` to the token from the result makes `apply` refuse the commit when another edit landed in between. In that case, evaluate again.

If you scored with `clearFirst: true` in the evaluate options, commit with `level` and its own `clearFirst` left at the default `true`. The commit then re-levels from zero, like the scoring did.

To handle a rejected `apply`, see [Recover from rejected changes](<https://docs.dhtmlx.com/planning-engine/wasm/how-to/recover-from-rejected-changes.md>). To generate candidates automatically instead of writing them by hand, use [`suggestAssignments`](<https://docs.dhtmlx.com/planning-engine/wasm/api/project-suggest-assignments.md>), which scores its steps the same way. See [Suggesting assignments](<https://docs.dhtmlx.com/planning-engine/wasm/resources-and-assignment/suggesting-assignments.md>).