Explanation:

The program is very simple, we have to take a variable and return that variable being repeated certain amount of times. No need to add space or anything, just keep repeating it into one single string.

Hint: 1

You can't edit strings, you will need to create a variable to store the new string.

Hint: 2

Create a loop to repeat the code as many times as needed.

Hint: 3

Make the variable created store the current value and append the word to it.

Spoiler Alert!

Solution ahead!

Code Solution:

First Solution

function repeat(str, num) {
  var accumulatedStr = '';

  while (num > 0) {
    accumulatedStr += str;
    num--;
  }

  return accumulatedStr;
}

Second Solution

function repeat(str, num) {
  var newstr = [];
  for (var i = 0; i < num; i++) {
    newstr.push(str);
  }
  return newstr.join('');
}

repeat("abc", 3);

Third Solution

(using Recursion)

function repeat(str, num) {
  if(num < 0)
    return "";
  if(num === 1)
    return str;
  else
    return str + repeat(str, num - 1);
}

Fourth Solution

(Declarative approach)

function repeat(str, num) {
  return num >= 0 ? str.repeat(num) : "";
}

repeat("abc", 3);

Code Explanation:

First and Second solutions

Create a variable to store the repeated word.
Use a while loop or for loop to repeat code as many times as needed according to num
Then we just have to add the string to the variable created on step one. and increase or decrease num depending on how you set the loop.
At the end of the loop, return the variable for the repeated word.

Third solution

(using recursiveness)

We check if num is a negative and return an empty string if true.
Then we check if it's equal to 1 and in that case we return the string itself.
If not, we add the string to a call of our function with num being decreased by 1, which will add another str and another until eventually num is 1. And return that whole process.

Fourth solution