Javascript：如何获取function.apply（）的键

Question

I am trying to cache 'func.apply(this, func)' value so that it can be looked up later rather than running the function again. The problem is that I don't know how or what to use as the key.

Is there a way to assign an key of a function that can be looked up later?

Code example:

var m = function(func) {
  var cached = {};
  return function() {
    var key = ''; // how do I get or create the key of func.apply(this, func)?

    if (cached[key]) {
      return cached[key];
    }

    cached[key] = func.apply(this, arguments);
    return cached[key];
  };

};

The m() function should return a function that, when called, will check if it has already computed the result for the given argument and return that value instead if possible.

Answer 1

Why do you need an object with an index. Just store the result/key.

var m = function(func) {
    var result=null;
    return function() {
        if (result===null) {
            result = func.apply(this, arguments);
        }
        return result;
    }
};

But I am not sure that is what you want. If the function returns different values based on arguments, than you want to use a key based off the arguments.

 var m = function(func) { var results = {}; return function() { var key = [].slice.call(arguments).join("-"); if (results[key]===undefined) { results[key] = func.apply(this, arguments); } return results[key]; } }; var multiply = function (a,b) { return a * b; } var mult = m(multiply); console.log(mult(2,5)); //runs calculation console.log(mult(2,5)); //uses cache 

Answer 2

What are you looking for is called Memoization

See: Implementing Memoization in JavaScript

Here are an example:

var myFunction = (function() {
  'use strict';

  var functionMemoized = function() {
    // set the argumensts list as a json key
    var cacheKey = JSON.stringify(Array.prototype.slice.call(arguments));
    var result;

    // checks whether the property was cached previously
    // also: if (!(cacheKey in functionMemoized.cache))
    if (!functionMemoized.cache.hasOwnProperty(cacheKey)) {
        // your expensive computation goes here
        // to reference the paramaters passed, use arguments[n]
        // eg.: result = arguments[0] * arguments[1];
        functionMemoized.cache[cacheKey] = result;
    }

    return functionMemoized.cache[cacheKey];
  };

  functionMemoized.cache = {};

  return functionMemoized;
}());

Answer 3

If you send the value of the function as a string, you can use that as the index with one minor modification

var m = function(func, scope) {

  return function() {
    var cached = {};
    var index = func; // how do I get or create the index of func.apply(this, func)?
    scope = scope || this;
    if (!cached[index]) {
        func = scope[func]; //Get the reference to the function through the name
        cached[index] = func.apply(this, func);          
    }

    return cached[index];
  };

};

This does depend on if the index exists in the this object reference. Otherwise you should use a different scope.