Use Bracket Notation to Find the Last Character in a String.. Why -1?

JavaScript
1

Tell us what’s happening:
I’m just confused on why you subtract one? What is the purpose… I’m lost and just trying to understand why

Your code so far


// Example
var firstName = "Ada";
var lastLetterOfFirstName = firstName[firstName.length - 1];

// Setup
var lastName = "Lovelace";

// Only change code below this line.
var lastLetterOfLastName = lastName;

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Link to the challenge:
https://learn.freecodecamp.org/javascript-algorithms-and-data-structures/basic-javascript/use-bracket-notation-to-find-the-last-character-in-a-string

2

Remember that the characters in a string are like the elements of an array. Like an array the elements start at zero. So “Ada” would be 3 characters in length, but because the index starts at zero the last character would be at position 2.

1 Like
4

Thanks for replying! Just double checking that I understand so…

  1. Ada (A=0, d=1, a = 2)
  2. Ada length = 3
  3. 3-2=1 (This is where you get the -1)
5

Almost. Point #3 Length, which is 3 - 1 = 2.
The last letter in string “Ada” is in position 2. [0, 1, 2]

So, when you write: firstName[firstName.length - 1];
you are really saying: firstName[3 - 1] or firstName[2] which will be ‘a’

6

Typically, the term string is used to represent an array of characters… So the indices of characters in a string follow array like indices…

const string = 'Some String';`

Will be represented in memory as

['S', 'o', 'm', 'e', ' ', 'S', 't', 'r', 'i', 'n', 'g']
[ 0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ,  8 ,  9 ,  10]

Also str.length is 11.

Since indices start from 0 and length is 11, you last character is on 10th index. You last character’s index is always going to be 1 less that length of a string. Hence str.length - 1