Please explain me this higher-order function javascript code

Question

I'm studying higher order functions following the Eloquent JavaScript book. I haven't been able to understand this code, why is "Boolean" passed as noisy first argument?

This is supposed to be function that changes other function, I just don't get how it works!

function noisy(f) {   
    return function(arg) {     
        console.log("calling with", arg);     
        var val = f(arg);     
        console.log("called with", arg, "- got", val);     
        return val;   }; 
} 
noisy(Boolean)(0); 
// → calling with 0 
// → called with 0 - got false

Barmar · Accepted Answer · 2015-04-09 22:26:45Z

4

noisy accepts any one-argument function as its argument. It returns a new function that calls that function, but displays messages before and after it calls it.

Boolean is just an example function that they used. It converts its argument to a boolean datatype.

answered Apr 9, 2015 at 22:26

Barmar

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Comments

HankScorpio · Accepted Answer · 2015-04-09 22:28:39Z

0

Boolean is a constructor function for the Boolean type. It could be any function.

edited Apr 9, 2015 at 22:28

answered Apr 9, 2015 at 22:25

HankScorpio

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2 Comments

Barmar Over a year ago

It's not using new, it's just calling the Boolean function.

HankScorpio Over a year ago

Sorry, I wrote this hastily. Take Barmar's answer instead. As far as I can see, the noisy() function is pretty useless. What I really wanted to point out is that Boolean is a constructor function.

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