client_seprate_query_and_variables_mutation.js

var author = 'andy';
var content = 'hope is a good thing';
var query = `mutation CreateMessage($input: MessageInput) {
  createMessage(input: $input) {
    id
  }
}`;

fetch('/graphql', {
    method: 'POST',
    headers: {
        'Content-Type': 'application/json',
        'Accept': 'application/json',
    },
    body: JSON.stringify({
        query,
        variables: {
            input: {
                author,
                content,
            }
        }
    })
})
    .then(r => r.json())
    .then(data => console.log('data returned:', data));