Apply函数如何工作以读取传递给内部函数的所有数组参数？

Question

below i quote from eloquentJavascript

Passing along Arguments

function noisy(f) {
  return function(arg) {
    console.log("calling with", arg);
    var val = f(arg);
    console.log("called with", arg, "- got", val);
    return val;
  };
}

the above works for single argument and i got that part clear but what i would like to know is the phrase that comes after regarding apply method...it says we can pass an array-like argument list to the above function.... i tried doing it and failed... can anyone illustrate how to pass an array-like object of arguments and the function calling the arguments passed?

i saw the call, apply and bind functions from other sites but i would like to stick on this tutorial and see how it works here?

i run the above function as:

return noisy(String)(0); //works

return noisy(String).apply(null,[0,1,2,3,4]);

gets the same result as above:

calling with 0 called with 0 - got 0

how can i use apply to the noisy function to read all arguments?

Answer 1

See the bellow snippet

 // Code goes here function noisy(f) { return function() { var args = Array.prototype.slice.call(arguments); for(var i=0;i<args.length;i++){ console.log("calling with", args[i]); var val = f(args[i]); console.log("called with", args[i], "- got", val); } }; } noisy(String)(0); //works noisy(String).apply(null,[0,1,2,3,4]); 

Answer 2

You have to use the arguments object or the ES6 spread operator .

The second operator of apply expects an array, but it does not apply the array to your function. Instead it will call it by adding every array item as a parameter.