# Component IDs

A component has two types of IDs: a local ID and a global ID. You can retrieve a component using its local ID in your JavaScript code. A global ID can be useful to differentiate between multiple instances of a component or for debugging purposes.

## Local IDs

A local ID is an ID that is only scoped to the component. A local ID is often unique but it’s not required to be unique.

Create a local ID by using the `aura:id` attribute. For example:

```nolang
<lightning:button aura:id="button1" label="button1"/>

```

:::note
`aura:id` doesn't support expressions. You can only assign literal string values to `aura:id`.
:::

Find the button component by calling `cmp.find("button1")` in your client-side controller, where `cmp` is a reference to the component containing the button.

`find()` returns different types depending on the result.

- If the local ID is unique, `find()` returns the component.
- If there are multiple components with the same local ID, `find()` returns an array of the components.
- If there is no matching local ID, `find()` returns `undefined`.

To find the local ID for a component in JavaScript, use `cmp.getLocalId()`.

## Global IDs

Every component has a unique `globalId`, which is the generated runtime-unique ID of the component instance. A global ID (1) is not guaranteed to be the same beyond the lifetime of a component, so it should never be relied on. A global ID can be useful to differentiate between multiple instances of a component or for debugging purposes.

![Every component has a unique global ID.](https://a.sfdcstatic.com/developer-website/sfdocs/platform/media/aura-platform/globalID.png)

To create a unique ID for an HTML element, you can use the `globalId` as a prefix or suffix for your element. For example:

```nolang
<div id="{!globalId + '_footer'}"></div>
```

In your browser’s developer console, retrieve the element using `document.getElementById("<globalId>_footer")`, where `<globalId>` is the generated runtime-unique ID.

To retrieve a component’s global ID in JavaScript, use the `getGlobalId()` function.

```javascript
var globalId = cmp.getGlobalId();
```

**See Also**

- [Finding Components by ID](/docs/platform/aura-platform/guide/js-cb-find-by-id.md)
- [Which Button Was Pressed?](/docs/platform/aura-platform/guide/js-cb-which-button-pressed.md)