# Replace vs Replace All

There is a good chance that `replace` does not work how you think:

```javascript
const numbers = "10.00.00.0000"

const replaced = numbers.replace(".", "_")
console.log(replaced) // '10_00.00.0000'
```

Wait what? It only replaced the first instant, `replace` is a simple function and expects you to pass a regular expression if you want more complex results. We can pass an expression that makes it run a global replacement like so:

```javascript
const numbers = "10.00.00.0000"

const globalReplace = numbers.replace(/\./g, "_");
console.log(globalReplace); // '10_00_00_0000'
```

It works, but do any of us really understand RegEx 🤪. Now, there is a more straightforward method.

```javascript
const numbers = "10.00.00.0000"

const replacedAll = numbers.replaceAll(".", "_")
console.log(replacedAll) // '10_00_00_0000'
```

The fantastic function `replaceAll` has full support across all browsers except IE; you can find the [full breakdown here](https://caniuse.com/?search=replaceAll).

**Update 20/10/2024:**

After posting on BlueSky, [Larry Williamson](https://bsky.app/profile/l422y.com) pointed out another method of replacing all occurrences in a string.

```javascript
const numbers = "10.00.00.0000"

const splitReplace = numbers.split(".").join("_")
console.log(splitReplace) // '10_00_00_0000'
```

The speed difference between them is negligible. You have to be parsing large strings before even getting close to a 0.01 millisecond difference in speed. Like all quick benchmarking using, [`performance.now`](http://performance.now)`()` take it with a pinch of salt. Personally, I will be reaching for `replaceAll` from now on.