let num = 17340164790;
let n = num.toString();
let NUM_U = n.replace(n.substring(3,7),‘****‘);
console.log(NUM_U);

let num = 17340164795;
let n = num.toString();
let NUM_U = n.substr(0,3) + ‘****‘ + n.substr(7,4);
console.log(NUM_U);

var tel = 18810399133;
tel = "" + tel;
var reg=/(\d{3})\d{4}(\d{4})/;
var tel1 = tel.replace(reg, "$1****$2");
console.log(tel1);