Question

How can we use java script to restrict the use of non-ascii characters in a specific text field..? thanks in advance…

Answer 1

Ascii is defined as the characters in the range of 000-177 (octal), therefore

function containsAllAscii(str) {
    return  /^[\000-\177]*$/.test(str) ;
}

console.log ( containsAllAscii('Hello123-1`11'));
console.log ( containsAllAscii('ábcdé'));

You probably don’t want to accept non-printing characters \000-\037, maybe your regex should be /\040-\176/