What is a question mark in graphql?

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What are the meanings of the various question marks here?

type GraphQLEnumValueDefinition = {
  name: string;
  value?: any;
  deprecationReason?: string;
  description?: ?string;
}

source: https://graphql.org/graphql-js/type/#graphqlenumtype

Are there other usages of question mark within graphql?

graphql
1 Answers

GraphQL.js is written using Flow, which is a static type checker that introduces some additional syntax on top of JavaScript. The ? indicates a Maybe Type which simply means the value is optional. So a property that has the string type must always be a string, while one with the ?string type could be a string, null or undefined.

Because GraphQL.js is written in Flow, it's generated documentation includes Flow syntax. However, this syntax is unrelated to GraphQL itself. ? is not a token in GraphQL syntax itself.

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