**// js**
/**
 * Validate input email
 * @param email
 * @returns {boolean}
 */
export const isValidEmailFormat = (email) => {
    const regex = /^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\\.[a-zA-Z0-9-]+)*$/
    return regex.test(email)
}

**// TypeScript**
/**
 * Validate input email
 * @param email
 */
export const isValidEmailFormat = (email: string): boolean => {
  const regex = /^[a-zA-Z0-9.!#$%&'*+\\/=?^_`{|}~-]+@[a-zA-Z0-9-]+(?:\\.[a-zA-Z0-9-]+)*$/; // eslint-disable-line no-useless-escape
  return regex.test(email);
};

▼呼び出し側

import {isValidEmailFormat} from "〜";

// signUp関数の引数には、inputのvalue（state）をセット
export const signUp = (username, email, password, confirmPassword) => {
    return async (dispatch) => {
        // Validations
        **if(!isValidEmailFormat(email)) {
            alert('メールアドレスの形式が不正です。もう1度お試しください。')
            return false
        }**
〜〜〜