console.log(add(1,2)(3))结果是6

let add = function(a,b){
    return function(c){
        return a+b+c
    }
}
console.log(add(1,2)(3))

console.log(add(1)(2，3))结果是6

let add = function(a){
    return function(b,c){
        return a+b+c
    }
}
console.log(add(1)(2,3))