Schema Custom - VkrunJS

Schema - custom

The .custom method adds custom validation logic to a schema. It enables full control over how a value is validated, and allows for value transformation if needed. You can implement custom logic either synchronously or asynchronously, depending on your validation flow.

Content

Quick Start

import { schema } from "vkrun";
 
const customSchema = schema()
  .string()
  .custom((ctx) => {
    if (ctx.value === "valid") {
      ctx.success(ctx.value);
    } else {
      ctx.failed("Validation failed");
    }
  });
 
console.log(customSchema.parse("valid")); // "valid"

Context Object

The callback provided to .custom() receives a context object with the following properties:

value: The current value being validated.
success(newValue): Marks the validation as successful, optionally transforming the value.
failed(message): Marks the validation as failed with an error message.

With Transformation

You can enforce a new output type by providing a generic type to .custom<T>().

const transformedSchema = schema()
  .string()
  .custom<number>((ctx) => {
    if (ctx.value === "convert") {
      ctx.success(42); // value becomes number
    } else {
      ctx.failed("Invalid input");
    }
  });
 
console.log(transformedSchema.parse("convert")); // 42

Async Support

The .custom() method supports async validation when used with testAsync(), parseAsync(), etc.

const asyncSchema = schema()
  .string()
  .custom(async (ctx) => {
    const isValid = await Promise.resolve(ctx.value === "yes");
 
    if (isValid) {
      ctx.success(ctx.value);
    } else {
      ctx.failed("Not allowed");
    }
  });
 
const result = await asyncSchema.parseAsync("yes");
console.log(result); // "yes"

Use .custom() when you need complete control over the validation logic, or when built-in methods are not enough to express your validation rules.

.number Introduction