CODE EXAMPLE FOR JAVASCRIPT

username validation formik react yup

validationSchema: Yup.object({
        email: Yup.string()
            .min(8, 'Must be at least 8 characters')
            .max(20, 'Must be less  than 20 characters')
            .required('Email is required')
            .test('Unique Email', 'Email already in use', // <- key, message
                function (value) {
                    return new Promise((resolve, reject) => {
                        axios.get(`http://localhost:8003/api/u/user/${value}/available`)
                            .then((res) => {
                                resolve(true)
                            })
                            .catch((error) => {
                                if (error.response.data.content === "The email has already been taken.") {
                                    resolve(false);
                                }
                            })
                    })
                }
            ),
    }),