> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/upstash/redis-js/llms.txt
> Use this file to discover all available pages before exploring further.

# set

> Set the string value of a key

## Description

Set key to hold the string value. If key already holds a value, it is overwritten, regardless of its type. Any previous time to live associated with the key is discarded on successful SET operation.

## Syntax

```typescript theme={null}
redis.set<TData>(
  key: string,
  value: TData,
  opts?: SetCommandOptions
): Promise<TData | "OK" | null>
```

## Parameters

<ParamField path="key" type="string" required>
  The key to set
</ParamField>

<ParamField path="value" type="TData" required>
  The value to store. Can be a string, number, object, or any serializable data
</ParamField>

<ParamField path="opts" type="SetCommandOptions">
  Optional configuration for the SET command

  <Expandable title="properties">
    <ParamField path="ex" type="number">
      Set the specified expire time, in seconds (a positive integer)
    </ParamField>

    <ParamField path="px" type="number">
      Set the specified expire time, in milliseconds (a positive integer)
    </ParamField>

    <ParamField path="exat" type="number">
      Set the specified Unix time at which the key will expire, in seconds (a positive integer)
    </ParamField>

    <ParamField path="pxat" type="number">
      Set the specified Unix time at which the key will expire, in milliseconds (a positive integer)
    </ParamField>

    <ParamField path="nx" type="boolean">
      Only set the key if it does not already exist
    </ParamField>

    <ParamField path="xx" type="boolean">
      Only set the key if it already exists
    </ParamField>

    <ParamField path="keepTtl" type="boolean">
      Retain the time to live associated with the key
    </ParamField>

    <ParamField path="get" type="boolean">
      Return the old string stored at key, or `null` if key did not exist
    </ParamField>
  </Expandable>
</ParamField>

## Type Parameters

<ParamField path="TData" type="type">
  The type of the value being stored
</ParamField>

## Returns

<ResponseField name="result" type="TData | 'OK' | null">
  * Returns `"OK"` if SET was executed correctly
  * Returns `null` if the SET operation was not performed (due to `nx` or `xx` conditions)
  * Returns the old value if the `get` option was specified
</ResponseField>

## Examples

### Basic Usage

```typescript theme={null}
import { Redis } from '@upstash/redis';

const redis = new Redis({
  url: 'https://your-redis-url.upstash.io',
  token: 'your-token'
});

// Simple string set
await redis.set('greeting', 'Hello, World!');
// Returns: "OK"

// Set a number
await redis.set('counter', 42);
// Returns: "OK"
```

### Set with Expiration

```typescript theme={null}
// Expire in 60 seconds
await redis.set('session:abc', 'user-data', { ex: 60 });

// Expire in 5000 milliseconds
await redis.set('temp:key', 'value', { px: 5000 });

// Expire at specific Unix timestamp (seconds)
const expirationTime = Math.floor(Date.now() / 1000) + 3600; // 1 hour from now
await redis.set('token', 'secret-token', { exat: expirationTime });

// Expire at specific Unix timestamp (milliseconds)
const expirationTimeMs = Date.now() + 3600000; // 1 hour from now
await redis.set('token', 'secret-token', { pxat: expirationTimeMs });
```

### Conditional Set

```typescript theme={null}
// Only set if key doesn't exist (SET NX)
const result1 = await redis.set('key', 'value', { nx: true });
console.log(result1); // "OK" if key didn't exist, null otherwise

// Only set if key exists (SET XX)
const result2 = await redis.set('key', 'new-value', { xx: true });
console.log(result2); // "OK" if key existed, null otherwise
```

### Set and Get Old Value

```typescript theme={null}
// Set initial value
await redis.set('score', 100);

// Set new value and get the old one
const oldValue = await redis.set('score', 200, { get: true });
console.log(oldValue); // 100
```

### Working with Objects

```typescript theme={null}
interface User {
  id: number;
  name: string;
  email: string;
}

const user: User = {
  id: 1,
  name: 'Alice',
  email: 'alice@example.com'
};

// Store object with 1 hour expiration
await redis.set('user:1', user, { ex: 3600 });
```

### Keep TTL

```typescript theme={null}
// Set a key with expiration
await redis.set('key', 'value1', { ex: 300 }); // 5 minutes

// Update the value but keep the remaining TTL
await redis.set('key', 'value2', { keepTtl: true });
// The key still has the same remaining TTL from the first SET
```

## Notes

* The `ex`, `px`, `exat`, `pxat`, and `keepTtl` options are mutually exclusive
* The `nx` and `xx` options are mutually exclusive
* When using the `get` option, the command returns the old value instead of `"OK"`

## Related Commands

* [get](/api/commands/get) - Get the value of a key
* [mset](/api/commands/mset) - Set multiple keys to multiple values

## Redis Documentation

For more information, see the [Redis SET documentation](https://redis.io/commands/set).