Javascript module is variable in function not accessing the outer scope variable

Question

This is strange... in function getNumber() the variable mostRecent is not accessing the outer variable var mostRecent.

I see in console that console.log(mostRecent) is showing mostRecent is updated, but when I do elements.mostRecent it still shows the default value.

var elements = function () {

    var mostRecent = { "timeStamp" : "0" };
    var timeCollection = [];

    function getElements() {
        var trElements = document.getElementsByTagName("tr");

        for (var i = 1; i < trElements.length; ++i) {
            var obj = {
                "action" : trElements[i].children[5].textContent,
                "timeStamp" : trElements[i].children[8].textContent
            }
            timeCollection.push(obj);
        }
    }

    function getNumber() {
        timeCollection.forEach(function findRecent(element) {
            var timeStamp = moment(element["timeStamp"], "MMM. D, YYYY, h:m A");
            var mostRecentMoment = moment(mostRecent["timeStamp"], "MMM. D, YYYY, h:m A");
            if (moment(timeStamp).isAfter(mostRecentMoment)) { mostRecent = element; }
        });

        console.log(mostRecent);
    }

    function refresh() {
        getElements();
        getNumber();
    }

    return {
        mostRecent : mostRecent,
        refresh: refresh
    }
}();

elements.refresh();

jbabey · Accepted Answer · 2014-01-07 16:14:02Z

4

The property mostRecent will not automatically update when the internal variable mostRecent changes. Make it a function instead to get the latest version of the internal variable:

return {
    getMostRecent: function () { 
        return mostRecent; 
    },
    refresh: refresh
};

answered Jan 7, 2014 at 16:14

jbabey

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1 Comment

dman Over a year ago

Originally, in return { mostRecent : mostRecent }, was the { mostRecent : a variable holding a copy of the var mostRecent contents rather than a reference to the memory location?

bevacqua · Accepted Answer · 2014-01-07 16:13:54Z

2

You are doing this:

var foo = { bar: 1, baz: 2 };
var tar = foo;
foo = { poo: 3, par: 4 };

tar
// <- { bar: 1, baz: 2 }

Effectively losing the reference.

You could do:

var foo = { bar: 1, baz: 2 };
var thing = {
    get tar () { return foo; }
};
foo = { poo: 3, par: 4 };

thing.tar;
// <- { poo: 3, par: 4 }

Using getters can complicate your code, though. You may prefer to simply keep the reference "a level above".

var thing = {
    foo: { bar: 1, baz: 2 }
};
// just return thing
thing.foo = { poo: 3, par: 4 };

// as long as you use the reference to thing, foo will always be up to date
thing.foo;
// <- { poo: 3, par: 4 }

answered Jan 7, 2014 at 16:13

bevacqua

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