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Asim Zaidi
Asim Zaidi

Reputation: 28284

attached to a method? code understanding

In the codebase that I am trying to figure out, I see that a js file (myloopfile.js) being imported into another js file. I am trying to make sense of some of the code used there

this is myloopfile.js

function method1(value) {
    // return something 
}

var myLooper = function (obj, iterator, context) {
    var key;
    if (obj) {
        if (typeof obj === 'function') {
            for (key in obj) {
                if (key != 'prototype' && key != 'length' && key != 'name' && (!obj.hasOwnProperty || obj.hasOwnProperty(key))) {
                    iterator.call(context, obj[key], key);
                }
            }
        } else if (obj.forEach && obj.forEach !== forEach) {
            obj.forEach(iterator, context);
        } else if (isArrayLike(obj)) {
            for (key = 0; key < obj.length; key++)
                iterator.call(context, obj[key], key);
        } else {
            for (key in obj) {
                if (obj.hasOwnProperty(key)) {
                    iterator.call(context, obj[key], key);
                }
            }
        }
    }

    return obj;
};

……………………………………………………………………………….

the myLoop in myloopfile.js is called like this 

var looper = require(‘../myloopfile.js);

looper({
        loop1: function(Home) { //do something },
        loop2: function(Home) { //dosomething }
    }, function(return1, return2) {
        //do something else
    });

I am trying to find out where this 

function(return1, return2) {
        //do something else
});

coming from ? I don’t see anything in that file that suggests that there is a method attached to it. Also where are the parameters return1 and return2 coming from? is this some javascript way to attach things ?

Upvotes: 0

Views: 31

Answers (2)

Jakub Kotrs
Jakub Kotrs

Reputation: 6211

var myLooper = function (obj, iterator, context) {
    /* .... */
    iterator.call(context, obj[key], key);
    /* .... */
};

You pass:

looper({
    loop1: function(Home) { //do something },
    loop2: function(Home) { //dosomething }
}, function(return1, return2) {
    //do something else
});

So

obj = {
    loop1: function(Home) { //do something },
    loop2: function(Home) { //dosomething }
}

and

iterator = function(return1, return2) {
    //do something else
}

The Function.prototype.call() method calls a function with a given this value and arguments provided individually. Therefore, inside you iterator function:

this = context;
return1 = obj[key];
return2 = key;

Upvotes: 1

Jay
Jay

Reputation: 2686

So javascript has function that are called anonymous function that don't need a function name.

Basically it is used (in this instance) as a way to be an expantion of a parameter.

Take for example the javascript function setTimeout

Well setTimeout can take an anonymous function as one of its parameters i.e

var timer = setTimeout(function{
                          //do something
                         },
                       2000); 

 // setTimeout(function, time, paramters)

So you don't have to declare a function and pass it in as a parameter

Back to your case, you have this anonymous function that takes return1 and return2

So in the end:

  return1 = obj[key];
  return2 = key;

Upvotes: 1

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