# Using External JavaScript Libraries

To reference a JavaScript library, upload it as a static resource and use a `<ltng:require>` tag in your .cmp or .app markup.

:::note
Before you use a third-party JavaScript library, we recommend that you check [AppExchange](https://appexchange.salesforce.com/) for components or apps from Salesforce partners that match your requirements. Alternatively, check if a [base component](https://developer.salesforce.com/docs/component-library) provides your desired functionality.
:::

The framework’s content security policy mandates that external JavaScript libraries must be uploaded to Salesforce static resources.

You can’t use a `<script>` tag in a component. This restriction mitigates the risk of cross-site scripting attacks. You can add a `<script>` tag to an application’s template, which is a special type of component that extends `aura:template`.

:::note
Only third-party JavaScript libraries that are loaded via `ltng:require` are supported. Documentation and examples that demonstrate using a third-party JavaScript library don't constitute an endorsement of that library. We recommend that you check the third-party JavaScript library documentation for usage information.
:::

Here’s an example of using `ltng:require`.

```nolang
<ltng:require scripts="{!$Resource.resourceName}"
    afterScriptsLoaded="{!c.afterScriptsLoaded}" />
```

*resourceName* is the `Name` of the static resource. In a managed package, the resource name must include the package namespace prefix, such as $Resource.yourNamespace\_\_resourceName. For a stand-alone static resource, such as an individual graphic or script, you only need the name of the resource. For example, if you uploaded `myScript.js` and set the `Name` to `myScript`, reference it as `$Resource.myScript`. To reference an item within an archive static resource, add the rest of the path to the item using string concatenation.

The `afterScriptsLoaded` action in the client-side controller is called after the scripts are loaded and the component is rendered. Don’t use the `init` event to access scripts loaded by `ltng:require`. These scripts load asynchronously and are most likely not available when the `init` event handler is called.

Here are some considerations for loading scripts:

**Loading Sets of Scripts:** Specify a comma-separated list of resources in the `scripts` attribute to load a set of resources.

:::note
Due to a quirk in the way `$Resource` is parsed in expressions, use the `join` operator to include multiple `$Resource` references in a single attribute. For example, if you have more than one JavaScript library to include into a component the `scripts` attribute should be something like the following.

```nolang
scripts="{!join(',',
    $Resource.jsLibraries + '/jsLibOne.js',
    $Resource.jsLibraries + '/jsLibTwo.js')}"
```
:::

**Loading Order:** The scripts are loaded in the order that they are listed.

**One-Time Loading:** Scripts load only once, even if they’re specified in multiple `<ltng:require>` tags in the same component or across different components.

**Parallel Loading:** Use separate `<ltng:require>` tags for parallel loading if you have multiple sets of scripts that are not dependent on each other.

**Encapsulation:** To ensure encapsulation and reusability, add the `<ltng:require>` tag to every .cmp or .app resource that uses the JavaScript library.

`ltng:require` also has a `styles` attribute to load a list of CSS resources. You can set the `scripts` and `styles` attributes in one `<ltng:require>` tag.

## Using a Client-Side Controller with External JavaScript Libraries

If you’re using an external library to work with your HTML elements after rendering, use `afterScriptsLoaded` to wire up a client-side controller. The following example sets up a chart using the Chart.js library, which is uploaded as a static resource.

```nolang
<ltng:require scripts="{!$Resource.chart}"
              afterScriptsLoaded="{!c.setup}"/>
<canvas aura:id="chart" id="myChart" width="400" height="400"/>
```

The component’s client-side controller sets up the chart after component initialization and rendering.

```nolang
setup : function(component, event, helper) {
    var data = {
        labels: ["January", "February", "March"],
        datasets: [{
            data: [65, 59, 80, 81, 56, 55, 40]
        }]
    };
    var el = component.find("chart").getElement();
    var ctx = el.getContext("2d");
    var myNewChart = new Chart(ctx).Line(data);
}
```

## Troubleshooting Errors from `ltng:require`

Let’s say your component references a custom JavaScript library with `ltng:require`. When you try to load the component, a modal dialog interrupts and displays information about an error.

For example, the dialog could show a message like the following.

```nolang
Custom Script Eval error in 'ltng:require' [SecureDOMEvent: [object Event] {key: {namespace":"c"}}]
```

The dialog could also include a stack trace. If it doesn’t, check the browser’s JavaScript console for more information. If the component didn't load, the console doesn’t show much and the problem is likely in the library you referenced.

Use the [Locker Console](https://developer.salesforce.com/docs/component-library/tools/locker-service-console) to evaluate the JavaScript from the library to see if it’s affected by Locker restrictions.

If `ltng:require` encounters errors in your script, you see an error in the JavaScript console that includes details about the problem. The JavaScript console could show a message such as the following.

```nolang
WARNING: Failed to load script at
/resource/156768268766/MyHeader/static/myLib.js:
Cannot assign to read only property 'someProp' of object '[object Object]'
```

This also indicates the problem is in the static resource, `myLib.js` in this case. If the Locker Console gives you the same message when you evaluate the JavaScript from `myLib.js`, this confirms that the script is attempting to perform an action that is not allowed by Locker.

**See Also**

- [*Salesforce Help*: Static Resources](https://help.salesforce.com/apex/HTViewHelpDoc?id=pages_static_resources.htm)
- [$Resource](/docs/platform/aura-platform/guide/expr-resource-value-provider.md)
- [Using External CSS](/docs/platform/aura-platform/guide/apps-css-external-platform.md)
- [Lightning Component Library](/docs/platform/aura-platform/guide/component-library.md)
- [*Security for Lightning Components:* Content Security Policy Overview](https://developer.salesforce.com/docs/platform/lightning-components-security/guide/content-security-policy-intro.md)
- [Creating App Templates](/docs/platform/aura-platform/guide/apps-template-overview.md)