Demonstrates how to use JavaScript’s Proxy API to intercept function calls via the apply trap and implement simple caching (memoization) logic.

proxy-function-caching.js

const map = new Map()
const target = async (property: string) => {
    const random = (Math.random() * (2000 - 100)) + 100
    await new Promise(resolve => setTimeout(resolve, random))
    console.log(`fetch ${property} detail`)
    return Date.now()
}

const handler = {
    apply: async (target: (property: string) => Promise<number>, thisArg: unknown, argumentList: [ string ]): Promise<number> => {
        const property = argumentList[0]
        if (map.has(property)) {
            return map.get(property)
        }

        const data = await target.apply(thisArg, argumentList)
        map.set(property, data)

        return data
    },
}

async function test() {
    const proxy = new Proxy(target, handler)

    console.log(await proxy("1"))
    console.log(await proxy("1"))
    console.log(await proxy("1"))
    console.log(await proxy("2"))
}

test()