# Using JavaScript in PixieBrix
You might use JavaScript in PixieBrix to transform data for your custom needs.
To do this, you'll use the `Run JavaScript Function` brick.
### Writing Functions
To write a function, first add the `Run JavaScript Function` brick to your mod.
Inside the [Brick Configuration Panel](https://docs.pixiebrix.com/platform-overview/page-editor/page-editor-components/brick-configuration-panel), you can define a function, and pass arguments.
{% hint style="info" %}
Currently, the JavaScript brick only supports the native web API methods in Chrome. To check if a method will work, reference [Mozilla's Web APIs docs](https://developer.mozilla.org/en-US/docs/Web/API).
{% endhint %}
### Supplying Arguments
Most functions will require arguments to process data.
Specify the arguments in the Arguments field below the function. Click **Add Property** to create an item. You can reference variables and outputs from other bricks, arrays of data, strings, other objects, numbers, or boolean values.
### Referencing Arguments
You can reference defined arguments to the function in multiple ways (choose one):
Use `args`, like `function(args)` and set a const below the function like this: \
`const { arg1, arg2 } = args`;
If you'd like, you can also reference them directly via the params, like `function({arg1, arg2})` or you can avoid setting a `const` and reference arguments as `args.arg1` and `args.arg2`
### Converting JQ Filters to JavaScript with ChatGPT
If you've been using JQ in existing mods, you'll find ChatGPT is helpful in suggesting a JavaScript function for your JQ filter.
*JQ filters are used to transform input JSON data based on the user-defined script. JQ users create a filter to be performed on data. Whereas with JavaScript, you'll create a function and pass it arguments of data. If you're migrating from JQ bricks to JavaScript bricks, your data object will become your argument object, and you'll replace your filter with a function.*
Here's an example of how you could use ChatGPT to help you create a function from a JQ filter.
**Original JQ filter**
```jq
map({const: .Prompt, title: .Title})
```
**Prompt**
You can use a prompt like this:
```
i have this jq filter: map({const: .Prompt, title: .Title})
write a javascript function for it
```
**Output from ChatGPT**
```javascript
function jqFilterEquivalent(data) {
return data.map(item => ({
const: item.Prompt,
title: item.Title
}));
}
```
You might have to tweak it slightly, but ChatGPT is pretty good at giving you the JavaScript version.
{% hint style="info" %}
[Activate this mod](https://app.pixiebrix.com/activate?id=@pixie-britt/developers/convert-jq-to-javascript) and use the Quick Bar to post a JQ filter and the sidebar will return its JavaScript equivalent!
{% endhint %}
### Troubleshooting/FAQs
#### My function isn't working. How can I tell if the error is in my JavaScript?
If you're experiencing any issues with your function, try running the function in a [JavaScript playground](https://jsfiddle.net/) to confirm there are no issues with the function.
#### Can I call multiple functions in one brick?
You can nest functions within the function, but you cannot have multiple top level functions in the same brick.
For example, this works: ✅
```javascript
function ({x, y}) {
function getSquared(z) {
return z ** 2;
}
return getSquared(x) + getSquared(y);
}
```
This does not: 🛑
```javascript
function getSquared(z) {
return z ** 2;
}
function ({x, y}) {
return getSquared(x) + getSquared(y);
}
```
#### I see Error running user-defined JavaScript Error in the brick run
Head to `Logs` tab, just above **Brick Actions** to see the specific error. The Page Editor don't expose this in the brick itself, but you'll be able to see details expanding the row with the error.
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