sample.js

// Don't
function handler(event, context) {
    const s3 = new AWS.S3()
    
    return s3.upload({}).promise()
}


// Better - Init variables outside the handler
const s3 = new AWS.S3()

function handler(event, context) {
    return s3.upload({}).promise()
}


// Example for in-memory caching
const cache = {}

function handler(event, context) {
    const now = Date.now()

    if ('userTypes' in cache && now < cache.userTypes.expiry) {
        // Data is cached and still fresh
        // One less database query.        
        return userTypes.data
    }
        
    // Reset cache with fresh data.
    cache.userTypes = {
        data: getUserTypesFromDatabase,
        expiry: now + TWO_HOURS
    }
    
    return cache.userTypes
}