Insert a string at a specific index

Question

How can I insert a string at a specific index of another string?

 var txt1 = \"foo baz\"

Suppose I want to insert \"bar \" after the \"foo

Answer 1

Using slice

You can use slice(0,index) + str + slice(index). Or you can create a method for it.

String.prototype.insertAt = function(index,str){
  return this.slice(0,index) + str + this.slice(index)
}
console.log("foo bar".insertAt(4,'baz ')) //foo baz bar

Splice method for Strings

You can split() the main string and add then use normal splice()

String.prototype.splice = function(index,del,...newStrs){
  let str = this.split('');
  str.splice(index,del,newStrs.join('') || '');
  return str.join('');
}


 var txt1 = "foo baz"

//inserting single string.
console.log(txt1.splice(4,0,"bar ")); //foo bar baz


//inserting multiple strings
console.log(txt1.splice(4,0,"bar ","bar2 ")); //foo bar bar2 baz


//removing letters
console.log(txt1.splice(1,2)) //f baz


//remving and inseting atm
console.log(txt1.splice(1,2," bar")) //f bar baz

Applying splice() at multiple indexes

The method takes an array of arrays each element of array representing a single splice().

String.prototype.splice = function(index,del,...newStrs){
  let str = this.split('');
  str.splice(index,del,newStrs.join('') || '');
  return str.join('');
}


String.prototype.mulSplice = function(arr){
  str = this
  let dif = 0;
  
  arr.forEach(x => {
    x[2] === x[2] || [];
    x[1] === x[1] || 0;
    str = str.splice(x[0] + dif,x[1],...x[2]);
    dif += x[2].join('').length - x[1];
  })
  return str;
}

let txt = "foo bar baz"

//Replacing the 'foo' and 'bar' with 'something1' ,'another'
console.log(txt.splice(0,3,'something'))
console.log(txt.mulSplice(
[
[0,3,["something1"]],
[4,3,["another"]]
]

))