Weird result in console: appends "undefined" to output

Question

I'm trying to complete The Odin Project and saw an interesting console error

function repeat(string, number) {
  var finalst;

  for (i = 0; i < number; i++) {
    finalst += string;

  }
  return finalst;
}
console.log(repeat("hey", 3));

The result in console is "undefinedheyheyhey". How is it showing like that and why ?

It's probably because `finalst` is initially set to the value `undefined`. To fix this, set the initial value of `finalst` to an empty string. — Edric, Jun 04 '20 at 14:10
[What's the difference between variable definition and declaration in JavaScript?](https://stackoverflow.com/questions/20822022/whats-the-difference-between-variable-definition-and-declaration-in-javascript#:~:text=What's%20the%20analog%20in%20JS,value%20to%20this%20allocated%20memory) — j08691, Jun 04 '20 at 14:12

Majed Badawi · Accepted Answer · 2020-06-04T14:20:04.650

5

You need to initialize it like this: var finalst = "";:

function repeat(string, number) {
  var finalst = ""; //change this

  for (i = 0; i < number; i++) {
    finalst += string;

  }
  return finalst;
}
console.log(repeat("hey", 3));

If you don't, it's initial value will be undefined, which will result in undefined+hey+hey+hey in your case:

var finalst;
console.log(finalst);
for (i = 0; i < 3; i++) {
    finalst += "hey";
}
console.log(finalst);

edited Jun 04 '20 at 14:20

answered Jun 04 '20 at 14:11

Majed Badawi

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1

Instead of only providing code to OP, please also explain _how_ your code has resolved the issue. – Edric Jun 04 '20 at 14:12

score 4 · Answer 2 · answered Jun 04 '20 at 14:13

If you don't init value, it's value = undefined.

finalst += string;: finalst.toString() + string => undefined + hey

You need init finalst:

function repeat(string, number) {
  var finalst = "";

  for (i = 0; i < number; i++) {
    finalst += string;

  }
  return finalst;
}
console.log(repeat("hey", 3));

Weird result in console: appends "undefined" to output

2 Answers2