Create a method in an involved function

Question

The javascript allows you to create involve functions as can be seen in that SOEN response and in that reply.

With the help of these answers I managed to involve a function spy, as in the code below:

function spy(func) {
  return function(){
    var args = Array.prototype.slice.call(arguments);
    return func.apply(this, args);
  }
}

what I want to do now is this, when I assign this "wrapper" (wrapper), I want it to have an accessible object that generates me a report, for example:

var spied = spy(umaFuncao);
var report = spied.report();

And this object has accessible properties, such as the number of times the method involved has been called, for example:

console.log(report.totalCalls);//Será impresso no console o número de vezes que o método foi chamado

How could I do that? This is a question that can be found in codewars and I thought it would be interesting to bring here.

Answer 1

You can hang the properties you want to monitor on the object/function that is returning. For example:

function spy(func) {
    function spied(){
        var args = Array.prototype.slice.call(arguments);
        spied.totalCalls++;
        return func.apply(this, args);
    }
    spied.totalCalls = 0;
    return spied;
}

var spied = spy(function(){});

spied();
spied();
spied();

console.log(spied.totalCalls);

^{http://jsfiddle.net/8k4ph/1/}

If you really care about a method and the object report, take advantage of the closure being created:

function spy(func) {
    var report = { totalCalls: 0 };
    function spied(){
        var args = Array.prototype.slice.call(arguments);
        report.totalCalls++;
        return func.apply(this, args);
    }
    spied.report = function() {
        return report;
    }
    return spied;
}

var spied = spy(function(){});
var report = spied.report();

spied();
spied();
spied();

console.log(report.totalCalls);

^{http://jsfiddle.net/8k4ph/2/}