Join the string with same separator used to split

Question

I have a string that need to be split with a regular expression for applying some modifications.

eg:

const str = \"Hello+Beautiful#World\";
const spl         


        

Answer 1

My solution is to get the splitters then save them into an array and rejoin:

function splitAndRejoin(){
    const str = "Hello+Beautiful#World";
    const splited = str.split(/[\+#]/);
    var spliterCharacter = [];
    for(var i = 0; i < str.length; i++){
        if(str[i] == "+" || str[i] == "#"){
            spliterCharacter.push(str[i]);
        }
    }
    var rejoin = "";
    for (i = 0; i <= spliterCharacter.length; i++) {
        if(i< spliterCharacter.length)
            rejoin += splited[i] + spliterCharacter[i];
        else
            rejoin += splited[i];
    }
    console.log(splited);
    console.log(spliterCharacter);
    console.log(rejoin); // Result
}

Answer 2

Don't use split and join in this case. Use String.replace(), and return the modified strings:

const str = "Hello+Beautiful#World";

let counter = 1;
const result = str.replace(/[^\+#]+/g, m =>
  `${m.trim()}${String(counter++).padStart(3, '0')}`
);

console.log(result);

Another option, which might not fit all cases, is to split before the special characters using a lookahead, map the items, and join with an empty string:

const str = "Hello+Beautiful#World";

let counter = 1;
const result = str.split(/(?=[+#])/)
  .map(s => `${s.trim()}${String(counter++).padStart(3, '0')}`)
  .join('')

console.log(result);

Answer 3

you can rejoin the array by finding the indexes that where the matching happened on the string

const str = "Hello+Beautiful#World";
const regex = /[\+#]/g;
const splited = str.split(regex);
console.log(splited);


//join
let x = '';
let i=0;
while ((match = regex.exec(str)) != null) {
    x = x + splited[i] + "00" + (i+1) + str[match.index];
    i++;
}
x = x + splited[splited.length-1] + "00" + (i+1);
console.log(x);

Answer 4

You could get the missing substrings by iterating the splitted value and check the parts.

var string = "Hello++#+Beautiful#World",
    splitted = string.split(/[\+#]+/),
    start = 0,
    symbols = splitted.map((s, i, { [i + 1]: next }) => {
        var index = string.indexOf(next, start += s.length);
        if (index !== -1) {
            var sub = string.slice(start, index);
            start = index;
            return sub;
        }
        return '';
    });

console.log(symbols);
console.log(splitted.map((s, i) => s + symbols[i]).join(''));

Answer 5

When you place a pattern inside a capturing group, split will return the matched delimiters as even array items. So, all you need to do is modify the odd items:

var counter=1;
var str = "Hello+Beautiful#World";
console.log(
  str.split(/([+#])/).map(function(el, index){
    return el + (index % 2 === 0 ? (counter++ + "").padStart(3, '0') : '');
  }).join("")
);