how to push string in string code example

Example 1: insert string in string java

String newString = originalString.substring(0, index + 1) 
                           + stringToBeInserted 
                           + originalString.substring(index + 1);

Example 2: string concatenation in js

var str1 = "Hello ";
var str2 = "world!";
var res = str1.concat(str2);
console.log(res);