Lists

Let's explore some techniques for working with Redis lists within Node. Instead of a list of fruits, let's work with vegetables this time:

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Add an Element to a List

Here's the code to add a to a Redis list with a key called veggies:

const Redis = require('ioredis');

const redis = new Redis();

async function main() {
    const key = 'veggies';
    const vegetable = 'tomato';
    try {
        const result = await redis.rpush(key, vegetable);
        console.log(result);
    } catch (error) {
        console.error(error);
    }
    redis.disconnect();
}

main();

If the rpush command is successful in line 9, the number of items in the list (after adding the new item) is displayed in line 10.

Add Multiple Elements to a List

Let's add a JavaScript array of vegetables to our list:

const Redis = require('ioredis');

const redis = new Redis();

async function main() {
    const key = 'veggies';
    const veggies = ['tomato', 'corn', 'eggplant'];
    try {
        const result = await redis.rpush(key, ...veggies);
        console.log(result);
    } catch (error) {
        console.error(error);
    }
    redis.disconnect();
}

main();

In line 8, notice that we use the JavaScript Spread syntax to expand the veggies array into multiple arguments to be passed to the rpush function. This enables us to push all the vegetable elements to the redis list in one operation. As a less elegant approach, we could have looped through the veggies array, and pushed each vegetable element one-by-one.

Remove an Element from a List

Next, we remove an element from the list using rpop:

const Redis = require('ioredis');

const redis = new Redis();

async function main() {
    const key = 'veggies';
    try {
        const veggie = await redis.rpop(key);
        console.log(veggie);
    } catch (error) {
        console.error(error);
    }
    redis.disconnect();
}

main();

In line 8, the rpop command removes and returns the last element of the veggies list, and stores it in the veggie variable.

Return all Elements in a List

We can use the lrange command to return a JavaScript array of elements from a list:

const Redis = require('ioredis');

const redis = new Redis();

async function main() {
    const key = 'veggies';
    try {
        const veggies = await redis.lrange(key, 0, -1);
        veggies.forEach(v => console.log(v));
    } catch (error) {
        console.error(error);
    }
    redis.disconnect();
}

main();

In line 8, we use a start value of 0 and a stop value of -1 to return all elements in the Redis list.