How To Replace At The Particular Range Of Indexes?

I have a string like this: var str = 'this is test1 this is test2 this is test3 this is test4'; Now I want to append 4 spaces before every lines w

Solution 1:

You can use replace with callback:

var str = "this is test1\n"+
           "this is test2\n"+
           "this is test3\n"+
           "this is test4";

var posStart = 14; // start index
var posEnd   = 40; // end index
var re = new RegExp(
  '^([\\s\\S]{' + (posStart-1) + '})([\\s\\S]{' + (posEnd-posStart+1) + '})');
//=> re = /^([\s\S]{13})([\s\S]{27})/

var r = str.replace(re, function($0, $1, $2) {
    return $1+$2.replace(/\n/g, '\n    '); });

console.log(r);
/* 
"this is test1
    this is test2
    this is test3
this is test4"
*/

Regex ^([\s\S]{13})([\s\S]{27}) makes sure replacement happens between position 14-40 only.

Solution 2:

You can try something like this:

Also note, its not a good option to check for char index for logic.

function addSpaces(){
  var str = "this is test1\n"+
            "this is test2\n"+
            "this is test3\n"+
            "this is test4"
  var data = str.split("\n");
  
  var result = data.map(function(item, index){
    if(index >0 && index < data.length-1){
      item = "    " + item;
    }
    return item;
  }).join("\n");
  
  console.log(result)
}

addSpaces();