parseThenable

Parses a value into a thenable (Promise-like) object. This parser combines the validateThenable protocol validator with the normalizeThenable normalizer to ensure that the input is an object or function with a callable then property.

The parser never throws, never mutates input, and never invokes the then method. It returns a structured ParseResult<PromiseLike<T>> describing success or failure.

Signature

function parseThenable<T = unknown>(
    value: unknown
): ParseResult<PromiseLike<T>>

Behavior

• Accepts:
• Native Promises
• Custom thenables
• Objects or functions with a callable then property
• Rejects:
• Primitives.
• null and undefined.
• Objects without a callable then.
• Functions without a then property.
• Never invokes then.
• Never wraps values or creates Promises.
• Never throws and never mutates input.

Returns

• ok: true And the original thenable when parsing succeeds.
• ok: false, value: null: And a list of issues when parsing fails.

Examples

parseThenable(Promise.resolve(1))
// { ok: true, value: Promise(1), issues: [] }

parseThenable({ then: () => {} })
// { ok: true, value: { then: [Function] }, issues: [] }

parseThenable(123)
// { ok: false, value: null, issues: ["Value is not a thenable (Promise-like) object"] }

Notes

• This parser is ideal for safely handling Promise-like values without triggering execution.
• Useful for async pipelines, lazy evaluation, and interoperability with libraries that implement custom thenables.