SOURCE

function Reg (item_decimal) {return ('^(ND|NK|-?([0-9]+' + (item_decimal > 0 ? ('(\\' + '.[0-9]' + '{1,' + item_decimal + '})?') : '')) + '))$'}

const reg = new RegExp(Reg(2));

console.log(reg.test(2.222))

console.log(Reg(2))

// ^(ND|NK|-?([0-9]+(\.[0-9]{1,2})?)$

//  var regexp = new RegExp(
//           `^(ND|NK|-?([0-9]+${m > 0 ? `(\\.[0-9]{1,${m}})?` : ''}))$`
//         )

function Role(item_decimal) {return 'Only ND/NK/number(up to ' + item_decimal + ' decimal places) is allowed'}