To replace the last character in a string call the `slice()` method passing it a start index of `0` and an end index of `-1` to get a part of the string up to the last character. Use the `+` operator to append the replacement character to the string.

Replace the Last Character in a String in JavaScript


## Replace the last character in a String

**To replace the last character in a string:**

1. Call the `slice()` method, passing it a start index of `0` and an end index
   of `-1` to get a string, containing the characters up to the last one.
2. Use the `+` operator to append the replacement character to the string.

```javascript:index.js
const str = 'Hello World.';

const replaced = str.slice(0, -1) + '!';
console.log(replaced); // 👉️ Hello World!
```

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<Alert>
  Indexes are zero-based in JavaScript. The first character in a string has an
  index of <code>0</code> and the last an index of <code>str.length - 1</code>.
</Alert>

The parameters we pass to the
[String.slice](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/slice)
method are:

1. **start index** - the index of the first character to be included in the
   returned string.
2. **end index** - go up to, but not including this index. A negative index
   indicates an offset from the end of the string.

<Alert>
  Passing a negative index parameter of <code>-1</code> and{' '}
  <code>str.length - 1</code> is the same. We instruct the <code>slice</code>{' '}
  method to go up to, but not including the last character in the string.
</Alert>

By getting a part of the string up to, but not including the last character, we
are able to replace it with one or more characters.

**This approach also works if we need to replace the last character with
multiple characters.**

```javascript:index.js
const str = 'Hello World.';

const replaced = str.slice(0, -1) + '!!!';
console.log(replaced); // 👉️ Hello World!!!
```

Note that the `slice` method does not change the contents of the original
string, it returns a new string containing a part of the original string.

An alternative, but also very common approach is to use the
[String.replace](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/replace)
method.

**To replace the last character in a string:**

1. Call the `replace()` method, passing it a regular expression that matches the
   last character in the string and the replacement character as parameters.
2. The `replace` method will return a new string with the last character
   replaced.

```javascript:index.js
const str = 'Hello World.';

const replaced = str.replace(/.$/, '!');
console.log(replaced); // 👉️ Hello World!
```

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The parameters we passed to the `replace` method are:

1. a regular expression to match in the string
2. a string replacement for the first match of the regular expression

If you ever need help reading a regular expression, check out this
[regular expression cheatsheet](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Cheatsheet)
by MDN.

The `.` character in our regular expression matches any single character.

The `$` character matches the end of a string.

This satisfies our requirement to match and replace the last character in the
string.

<Alert>
  The <code>replace</code> method does not mutate the original string, it
  returns a new string. Strings are immutable in JavaScript.
</Alert>

I prefer the first approach over using the `replace` method, because many
developers are not familiar with regular expressions.

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Replace the Last Character in a String in JavaScript

Replace the last character in a String #

Borislav Hadzhiev

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Replace the Last Character in a String in JavaScript