编写一个函数，其中“ sum（2,3）”和“ sum（2）（3）”的输出均为5

Question

Recently I come up with a question in an interview which is "write a function which will output of these two will same sum(2,3) and sum(2)(3), that is 5".

Please give any idea if it is possible.

Thanks in advance

Answer 1

For sum(x)(y) , have sum(x) return another function, f, such that f(y) - ie. (sum(x))(y) - evaluates to the correct result. See Eloquent JavaScript: Higher-Order Functions for examples on how closures - and returning functions from functions - make this possible.

The arguments.length property can be used to determine how many arguments have been supplied to the ( sum ) function and react accordingly: either the immediate sum, for sum(x, y) , or the aforementioned 'curried' function when invoked with a singular argument.

(The linked "Curried JavaScript functions: no, not curried spicy, but curried lambda-calculus-like" article actually contains a solution in full.. but it feels that to provide the code here would be cheating.)

Answer 2

Here's your simple function without counting the args:

function sum(a,b){
    if(b===undefined){
        return function(c){ return parseInt(a)+parseInt(c);}
    }
    return parseInt(a)+parseInt(b);
}
console.log(sum(2,3));
console.log(sum(2)(3));