understanding Formik and React - reactjs

Question

This is probably not the best place to post this question but where, then?
The code below is taken from Formik's overview page and I'm very confused about the onSubmit handlers:
The form element has an onSubmit property that refers to handleSubmit which is passed on that anonymous function : <form onSubmit={handleSubmit}>. Where does that come from?
The Formik component has an onSubmit property as well:
onSubmit={(values, { setSubmitting }) => { ... }
How do these relate to each other? What is going on?
import React from 'react';
import { Formik } from 'formik';
const Basic = () => (
<div>
<h1>Anywhere in your app!</h1>
<Formik
initialValues={{ email: '', password: '' }}
validate={values => {
let errors = {};
if (!values.email) {
errors.email = 'Required';
} else if (
!/^[A-Z0-9._%+-]+#[A-Z0-9.-]+\.[A-Z]{2,}$/i.test(values.email)
) {
errors.email = 'Invalid email address';
}
return errors;
}}
onSubmit={(values, { setSubmitting }) => {
setTimeout(() => {
alert(JSON.stringify(values, null, 2));
setSubmitting(false);
}, 400);
}}
>
{({
values,
errors,
touched,
handleChange,
handleBlur,
handleSubmit,
isSubmitting,
/* and other goodies */
}) => (
<form onSubmit={handleSubmit}>
<input
type="email"
name="email"
onChange={handleChange}
onBlur={handleBlur}
value={values.email}
/>
{errors.email && touched.email && errors.email}
<input
type="password"
name="password"
onChange={handleChange}
onBlur={handleBlur}
value={values.password}
/>
{errors.password && touched.password && errors.password}
<button type="submit" disabled={isSubmitting}>
Submit
</button>
</form>
)}
</Formik>
</div>
);
export default Basic;

Answer 1

The component takes onSubmit as a prop where you can execute code you want to perform when you submit your form. This prop is also given some arguments such as values (values of the form) for you to use in your onSubmit function.
The handleSubmit form is auto generated from the Formik library that automates some common form logics explained here. The handleSubmit will automatically execute onSubmit function mentioned above as part of its phases (pre-submit, validation, submission). Hope that answers your question!