Creates a lazy schema.

const Schema = v.lazy<TGetter>(getter);



  • getter TGetter


The getter function is called lazily to retrieve the schema. This is necessary to be able to access the input through the first argument of the getter function and to avoid a circular dependency for recursive schemas.



The following examples show how lazy can be used.

Binary tree schema

Recursive schema to validate a binary tree.

Due to a TypeScript limitation, the input and output types of recursive schemas cannot be inferred automatically. Therefore, you must explicitly specify these types using BaseSchema.

type BinaryTree = {
  element: string;
  left: BinaryTree | null;
  right: BinaryTree | null;

const BinaryTreeSchema: v.GenericSchema<BinaryTree> = v.object({
  element: v.string(),
  left: v.nullable(v.lazy(() => BinaryTreeSchema)),
  right: v.nullable(v.lazy(() => BinaryTreeSchema)),

Lazy union schema

Schema to validate a discriminated union of objects.

In most cases, union and variant are the better choices for creating such a schema. I recommend using lazy only in special cases.

const LazyUnionSchema = v.lazy((input) => {
  if (input && typeof input === 'object' && 'type' in input) {
    switch (input.type) {
      case 'email':
        return v.object({
          type: v.literal('email'),
          email: v.pipe(v.string(),,
      case 'url':
        return v.object({
          type: v.literal('url'),
          url: v.pipe(v.string(), v.url()),
      case 'date':
        return v.object({
          type: v.literal('date'),
          date: v.pipe(v.string(), v.isoDate()),
  return v.never();

The following APIs can be combined with lazy.






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