caolan/async · error · Error

async.auto task ` ` has a non-existent dependency ` ` in

Error message

async.auto task `${key}` has a non-existent dependency `${dependencyName}` in ${dependencies.join(', ')}

What it means

async.auto validates every dependency name listed in a task's dependency array against the tasks object. If a task declares a dependency that was never defined, auto throws immediately before running any task. This is an upfront graph validation to fail fast rather than deadlock or silently skip.

Solutions

1. Fix the dependency array to reference only keys that exist in the tasks object
2. Check for typos between task keys and dependency names
3. Log the generated tasks object keys before calling async.auto when building graphs dynamically
4. If the dependency is optional, remove it and coordinate ordering another way

Example fix

// before
async.auto({
  read: ['fil', readFile],
  data: ['read', processData]
});
// after
async.auto({
  read: ['file', readFile],
  data: ['read', processData]
});

function validateAutoTasks(tasks) {
  for (const [key, def] of Object.entries(tasks)) {
    const deps = Array.isArray(def) ? def[0] : [];
    for (const d of deps) {
      if (!tasks[d]) throw new Error(`Task '${key}' depends on unknown task '${d}'`);
    }
  }
}

try {
  await async.auto(tasks);
} catch (err) {
  if (String(err.message).includes('non-existent dependency')) {
    console.error('Task graph misconfigured:', err.message);
  } else throw err;
}

When it happens

Trigger: Calling async.auto({a: ['b', fn], b: fn2}) where task 'a' depends on 'b' but the dependency array contains a misspelled or undefined name, e.g. async.auto({read: ['fil', readFileFn]}) instead of 'file'. Also occurs when tasks are generated dynamically and a name is dropped.

Common situations: Typo in dependency names, renaming a task key without updating dependents, building the task graph from config where a step was removed, copy-paste between auto definitions.

Understand the failure class

Background: "not installed", "pip install", "required for": how missing-dependency errors surface across open-source libraries — this error's family across 34 libraries.

Related errors

• async.auto cannot execute tasks due to a recursive…
• autoInject task functions require explicit parameters.
• expected a function
• arity is undefined
• Callback was already called.

AI-assisted analysis of caolan/async@13dfaf13f3 (2026-08-28). Data as JSON: /api/errors/da88ee30318cedd4. Report an issue: GitHub.

Appendix: source

Thrown at lib/auto.js:200

        if (!Array.isArray(task)) {
            // no dependencies
            enqueueTask(key, [task]);
            readyToCheck.push(key);
            return;
        }

        var dependencies = task.slice(0, task.length - 1);
        var remainingDependencies = dependencies.length;
        if (remainingDependencies === 0) {
            enqueueTask(key, task);
            readyToCheck.push(key);
            return;
        }
        uncheckedDependencies[key] = remainingDependencies;

        dependencies.forEach(dependencyName => {
            if (!tasks[dependencyName]) {
                throw new Error('async.auto task `' + key +
                    '` has a non-existent dependency `' +
                    dependencyName + '` in ' +
                    dependencies.join(', '));
            }
            addListener(dependencyName, () => {
                remainingDependencies--;
                if (remainingDependencies === 0) {
                    enqueueTask(key, task);
                }
            });
        });
    });

    checkForDeadlocks();
    processQueue();

    function enqueueTask(key, task) {
        readyTasks.push(() => runTask(key, task));

View on GitHub (pinned to 13dfaf13f3)