一个函数如何操纵通过另一个函数传递的参数？ Java脚本

Question

Sorry, first attempt at explaining this question was poor. Trying to learn Javascript and a question from a code problem (codewars) has me stumped. It states, write a function that takes another function as a parameter and caches results so that if the same parameters are sent then the return is pulled from the cache and the actual function is not invoked again. For example:

var x = function(a, b) { a * b };
var cachedFunction = cache(x);

cachedFunction(4, 5); // function x should be executed
cachedFunction(4, 5); // function x should not be invoked again, instead the cached result should be returned
cachedFunction(4, 6); // should be executed, because the method wasn't invoked before with these arguments

I am not sure how to access the arguments sent via cachedFunction. The goal is to write cache so that it can handle a function x with any number of arguments.

Answer 1

What you're describing is not possible.

The expression x(5, 4) is evaluated before the cache() function is even called. It's not receiving a function. It's receiving the value 20 .

Answer 2

In your example, cache only has access to the return value of x . It can't know anything about how this return value was computed (ie by calling x with parameters 5, 4 ).

You would need to separately pass the function and its parameters to the cache function, eg as follows:

 function cache(func, ...params) { // Todo: do something with params return func(...params); } function x(a, b){ return a * b; } console.log(cache(x, 5, 4)); 

Answer 3

you can return a table like this:

function x(a,b){
    return [a, b, a*b];
}

after that you can get the params like this:

var result=x(values1,value2);
console.log(result[0]);// a == value1
console.log(result[1]);// b == value2
console.log(result[2]);// a*b == value1*value2