Support predefining types

(related to https://github.com/sindresorhus/query-string/issues/201)

Consider 2 examples:

const search1 = '?phoneNumber=%2B380951234567&subtopicId=2&topicId=1';
const result1 = queryString.parse(search, {
  parseBooleans: true,
  parseNumbers: true,
});

const search2 = '?phoneNumber=a%2B380951234567&subtopicId=2&topicId=1';
const result2 = queryString.parse(search, {
  parseBooleans: true,
  parseNumbers: true,
});

console.log('result1', result1);
// {
//   phoneNumber: 380951234567,
//   subtopicId: 2,
//   topicId: 1,
// };
console.log('result2', result2);
// {
//   phoneNumber: 'a+380951234567',
//   subtopicId: 2,
//   topicId: 1,
// };

In the 1st example, “+” sign (%2B escaped) is ignored thus reducing to the number parsing, which is not what it supposed to be.

The main goal is to keep parsing numbers for parameters which values starts on the number and parse as plain string otherwise.

Does it look feasible to make a PR on this or should I not use parseNumbers option in that case?

[sindresorhus]

I would prefer something like this:

const search2 = '?phoneNumber=a%2B380951234567&subtopicId=2&topicId=1';
const result2 = queryString.parse(search, {
    parseBooleans: true,
    parseNumbers: true,
    types: {
        phoneNumber: 'string',
        subtopicId: value => Number(value)
    }
});

The type could also be a function to let the user handle the converting it from a string to a custom type. Don’t forget that it also needs to be able to handle arrays.

[sindresorhus]

If anyone wants to work on this, see the feedback given in https://github.com/sindresorhus/query-string/pull/249.