---
title: "Set (Help Center / APIs & MCP / JS API)"
ai_context: "Use this article for questions about adding, setting, overwriting or enriching custom RUMvision data with the JavaScript API, `rumv('set', ...)`, set API, custom dimensions, custom values and request-level data. It covers setting a single value, setting multiple values, overwriting existing values, supported value types, custom dimension requirements, request data, PII sanitization and reading previously set values with `rumv('get', ...)`. Relevant for questions about release versions, deployment information, experiment or feature flags, checkout steps, custom metadata, arrays, booleans, numbers, strings and when custom data must be added before the relevant RUM beacon is sent."
canonical: "https://www.rumvision.com/help-center/apis/js/set/"
---

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# Set

The `set` API lets you add or overwrite data that RUMvision sends with a pageview.

> **Requirement:** Make sure the RUMvision JavaScript API is enabled. See [JavaScript API requirements](https://www.rumvision.com/help-center/apis/js/introduction/?format=md#requirement).

## Introduction

Use `set` for custom values that belong to the collected RUM data.

For example:

 ```
rumv('set', 'release', '2026.09.15');
```

Use `config` instead when you want to change how the RUMvision script itself behaves.

### Timing matters

Values added with `set` belong to the RUM data that is currently being collected.

Whenever possible, set values before RUMvision sends the relevant data. A value added later can still be included in a later beacon, but data that has already been finalized or sent cannot always be changed retroactively.

This is especially important when a value depends on consent.

For example, when storage consent is not available from the start, configure that before RUMvision initializes:

 ```
rumv('config', 'consent_storage', 0);
```

Then update the configuration when consent is granted:

 ```
rumv('config', 'consent_storage', 1);
```

### Reading values

Values written with `set` can be retrieved through `get`:

 ```
rumv('set', 'release', '2026.09.15');    rumv('get', 'release');  // '2026.09.15'
```

This makes it easy to inspect custom values during development without needing to know which internal object contains them.

## Set data

### Set a single value

By default, custom values are added to the current request. The key must correspond to a custom dimension that exists in your RUMvision configuration.

 ```
rumv('set', 'my_key', 'my value');
```

For example:

 ```
rumv('set', 'release', '2026.09.15');  rumv('set', 'checkout_step', 3);  rumv('set', 'feature_enabled', true);
```

The stored value is returned by the call.

### Set multiple values

You can pass an object to set multiple request values at once:

 ```
rumv('set', {  release: '2026.09.15',  checkout_step: 3,  feature_enabled: true  });
```

Do note:

- Each key is added to the current request data.
- Each key must correspond to an available custom dimension or will otherwise be ignored during data ingestion.
 
### Overwrite a value

`set` can overwrite an existing value:

 ```
rumv('set', 'checkout_step', 2);  rumv('set', 'checkout_step', 3);
```

The latest value becomes the value stored for that key.

## Where data is stored

Custom data is stored at request level. The field must first exist as a custom dimension in RUMvision. Internal field mapping is handled automatically.

### Request

Custom data is added to the current request:

 ```
rumv('set', 'my_key', 'my value');
```

The `request` type is the default and recommended target for custom data.

### Custom dimensions

Custom values are only stored when the field exists as a custom dimension in your RUMvision setup.

Create the custom dimension in RUMvision first, then use its configured name with `set`.

RUMvision handles the internal field mapping automatically.

Example:

 ```
rumv('set', 'release', '2026.09.15');
```

## Value types

### Supported values

Strings, numbers, booleans and arrays can be used directly:

 ```
rumv('set', 'release', '2026.09.15');  rumv('set', 'product_count', 4);  rumv('set', 'logged_in', true);  rumv('set', 'experiments', ['header-a', 'search-b']);
```

### Objects

When a plain JavaScript object is passed as a value, RUMvision converts its values to an array.

For example:

 ```
rumv('set', 'example', {  first: 'a',  second: 'b'  });
```

is stored as a value equivalent to:

 ```
['a', 'b']
```

If you need separate named fields, set them as separate keys instead.

### PII sanitization

Custom request values are passed through RUMvision's request-data sanitization when applicable.

This is especially relevant for values originating from application state, data layers or other user-controlled sources.

You should still avoid intentionally sending personally identifiable information to RUMvision.

## Examples

Add a release identifier:

 ```
rumv('set', 'release', '2026.09.15');
```

Add multiple values:

 ```
rumv('set', {  release: '2026.09.15',  deployment: 'blue',  feature_checkout: true  });
```

Add a value to the session-type payload:

 ```
rumv('set', 'experiment', 'variant-b', 'session');
```

Add a custom metric:

 ```
rumv('set', 'custom_metric', 123, 'metric');
```

## Return values

    Call Returns     `rumv('set', 'key', value)` The stored value   `rumv('set', { key: value })` The last stored value   Unknown custom dimension May be ignored during data ingestion