1、只调用一次函数

function once(fn) {
    let done = false
    return function () {
        if (!done) {
            done = true
            return fn.apply(this, arguments)
        }
    }
}
let pay = once(function (money) {
    console.log('money', money)
})
pay(5)
pay(4)

2、函数缓存

function getArea(r) {
    console.log('执行area')
    return Math.PI * r * r
}
function memoize(f) {
    let catche = {}
    return function () {
        let key = JSON.stringify(arguments)
        catche[key] = catche[key] || f.apply(f, arguments)
        return catche[key]
    }
}
let getAreaWithMemoize = memoize(getArea)
console.log(getAreaWithMemoize(4))
console.log(getAreaWithMemoize(4))
console.log(getAreaWithMemoize(4))