Create a string of specified copies of a given string

Question

I am trying to iterate over the original string 3 times. The result I get is: ["a","b","c","d",undefined,undefined,undefined,undefined,undefined,undefined,undefined,undefined,undefined,undefined,undefined,undefined]

The correct result should be: ["a", "b", "c", "d", "a", "b", "c", "d", "a", "b", "c", "d"]

function makeCopies (str, howmany) {
  let newCopy = [];
   for(let i = 0; i <  str.length * howmany; i++) {
   newCopy.push(str[i])
   } 
return newCopy;
}

console.log(makeCopies("abcd", 3))

I have tried many variations but nothing works, this is the closest I got.

`str.length * howmany` is 16. When you get to, say, `i = 6` you're doing `str[6]`. — VLAZ, Mar 09 '21 at 20:28
Already answered here: https://stackoverflow.com/questions/1877475/repeat-a-string-in-javascript-a-number-of-times — jburtondev, Mar 09 '21 at 20:31

score 4 · Accepted Answer · answered Mar 09 '21 at 20:29

4

JavaScript has a repeat Method on Strings. You can just use "abcd".repeat(3) and you will get "abcdabcdabcd". If you really want an array of the chars, you can spread the string into an array with [..."abcd".repeat(3)].

answered Mar 09 '21 at 20:29

Thomas Kay

229
1
2
5

score 2 · Answer 2 · answered Mar 09 '21 at 20:28

2

Javascript has a nice utility for this String.prototype.repeat. You can then split it on every character if an array is what you want.

console.log("abcd".repeat(3).split(""))

answered Mar 09 '21 at 20:28

Jonathan Hamel

1,393
13
18

Thanks, I was not aware of this one. – Miloš Leng Mar 09 '21 at 20:37

score 1 · Answer 3 · answered Mar 09 '21 at 20:29

1

The length of the array is becoming 12 when you multiply str.length * howmany, and when it gets further than the fourth value it can't find anything and so becomes undefined.

A solution is you can wrap the main loop in another loop which will run howmany times.

function makeCopies (str, howmany) {
   let newCopy = [];
   for (let i = 0; i < howmany; i++) {
       for(let j = 0; j <  str.length; j++) {
            newCopy.push(str[j])
        } 
    }
    return newCopy;
  }

  console.log(makeCopies("abcd", 3))

answered Mar 09 '21 at 20:29

Justin Feakes

380
1
7

I thought it would continue looping again through the same string., just like it does with arrays? Thanks. – Miloš Leng Mar 09 '21 at 20:36
1

Unfortunately it doesn't loop back over itself. The `for loop` in your question essentially looks like this: `for(let i = 0; i < 12; i++) {`, and so the loop will be looking for elements in the array at indexes higher than the indexes available in the array. – Justin Feakes Mar 09 '21 at 20:39
Thanks I understand now, great. – Miloš Leng Mar 09 '21 at 20:42
No worries mate. – Justin Feakes Mar 09 '21 at 20:43

score 1 · Answer 4 · answered Mar 09 '21 at 20:30

1

const makeCopies = (string, count) => new Array(count).join(string).split('');

console.log(makeCopies('abcd', 4))

answered Mar 09 '21 at 20:30

a.mola

3,883
7
23

score 1 · Answer 5 · answered Mar 09 '21 at 20:30

1

Why don’t you use repeat() ?

const res = "abc".repeat(3); // abcabcabc

If you need it as array, you can:

res.split(""); // ["a", "b", "c", ...]

answered Mar 09 '21 at 20:30

ikos23

4,879
10
41
60

score 0 · Answer 6 · answered Mar 09 '21 at 20:29

0

You are iterating outside the bounds of original string

str[i]; // i <  str.length * howmany;

Try create two cycles instead:

for(let i = 0; i < howmany; i++) {
  for(let j = 0; j < str.length; j++) {
    newCopy.push(str[j])
  }
}

answered Mar 09 '21 at 20:29

peter

583
2
11

Create a string of specified copies of a given string

6 Answers6