javascript - How do I type parseLiteral parameter in date scalar?

Question

How do I type ast?

import { CustomScalar, Scalar } from '@nestjs/graphql'
import { Kind } from 'graphql'
export class DateScalar implements CustomScalar<number, Date> {
  description = 'Date custom scalar type'

  parseValue(value: number): Date {
    return new Date(value) // value from the client
  }

  serialize(value: Date): number {
    return value.getTime() // value sent to the client
  }

  parseLiteral(ast): Date { // <-- ???
    if (ast.kind === Kind.INT) {
      return new Date(ast.value)
    }
    return null
  }
}

I tried to use

interface AST {
  kind: string
  value: number
}

but then I do get the error

  Property 'parseLiteral' in type 'DateScalar' is not assignable to the same property in base type 'CustomScalar<number, Date>'.
    Type '(ast: AST) => Date' is not assignable to type 'GraphQLScalarLiteralParser<Date>'.
      Types of parameters 'ast' and 'valueNode' are incompatible.
        Type 'ValueNode' is not assignable to type 'AST'.
          Property 'value' is missing in type 'VariableNode' but required in type 'AST'

question from:https://stackoverflow.com/questions/65644162/how-do-i-type-parseliteral-parameter-in-date-scalar

Answer 1

Okay, by looking at Nest's custom-scalar interface we can see that parseLiteral is of type GraphQLScalarLiteralParser<K> from graphql. After digging around GraphQL-js's types I found this definition where ast is also called a ValueNode. A ValueNode is a union of other value nodes that contains things like NullValueNode and ObjectValueNode which don't have value as properties, hence why you're getting that error.

All of that preface and linking to say: if you want to type it, use import { ValueNode } from 'graphql'; and use the type ValueNode. By using ast.Kind === Kind.INT the ast will get casted to an IntValueNode which has the field value as a property. Should clear up any type issues you've got