JAVASCRIPT

regex to check non empty string

/^(?!s*$).+/

regex to match empty string

/^$/ // match exactly ""

regex empty string

const REGEXP = /^$/;

const validate = (text) => {     
    return REGEXP.test(text);
}

const isEmpty = validate("");
const isNotEmpty = validate("x");

console.log(isEmpty); //true
console.log(isNotEmpty); //false

regex for non empty string

^(?!s*$).+

regex is not empty string

const REGEXP = /^$/;

const validate = (text) => {
    return REGEXP.test(text);
}

const isNotEmpty = validate("x");
const isEmpty = validate("");

console.log(isNotEmpty); //false
console.log(isEmpty); //true