Traversing a string in a loop — JavaScript fundamentals

You can use loops to process strings as well as numbers. Mainly as a method for retrieving a specific character by its index. Below is an example of code that prints each letter of a word on a single line:

const printNameBySymbol = (name) => {
  let i = 0;
  // This test works until a string ends,
  // including the last character. The last index is `length - 1`
  while (i < name.length) {
    // Get a character by its index
    console.log(name[i]);
    i = i + 1;
  }
};

const name = 'Arya';
printNameBySymbol(name);
// => 'A'
// => 'r'
// => 'y'
// => 'a'

The right test condition for the while loop is essential in this code. You can do it two ways: i < name.length or i <= name.length - 1. Both lead to the same result.

Building strings with loops

Loops also allow you to generate strings. It's a common task for web development. It's merely basic aggregation using interpolation or concatenation.

One especially popular task among interviewers is to do a string reversal. There are lots of ways to solve it, but the most basic is by iterating each character. Have a look at how this function works:

reverse('Hexlet'); // telxeH

The general idea of the reversal is that you take characters one by one from the beginning of the string and then connect them in reverse order. Sounds like a piece of cake. Now let's examine it:

const reverse = (str) => {
  let i = 0;
  // A neutral element in terms of strings is an empty string
  let result = '';
  while (i < str.length) {
    // Connect it in reverse order
    result = `${str[i]}${result}`;
    // Same through concatenation
    // result = str[i] + result;
    i = i + 1;
  }

  return result;
};

const name = 'Bran';
reverse(name); // 'narB'
// Testing neutral element
reverse(''); // ''

Perhaps the only tricky part here is getting a feel of how the string itself is built. Since each next character is attached to the resulting string on the left, the string ends up reversed.