How can I access variable inside another function jquery

Question

I have this object and want to access the variable scrolled var scrolled = 10; from the init function within the scrollDown function.

I am having trouble accessing the variable. How can I achieve this?

// Summary Screen Functions
var summary = {
    init: function() {

        var scrolled = 0;

        $('.page-summary-action a').on('click', summary.continueToSummary);
        $('.scroll-down').on('click', summary.scrollDown);
        $('.scroll-up').on('click', summary.scrollUp);
    },

    scrollDown: function(e) {
        e.preventDefault();
        scrolled = scrolled + 300;

        console.log('clicked');

        $(".data-cards").animate({
            scrollTop:  scrolled
        });
    },

    scrollUp: function(e) {
        e.preventDefault();
        console.log('clicked');

        $(".data-cards").animate({
            scrollTop: 15
        });
    }
};

summary.init();

Answer 1

var scrolled = 0; // Put the variable in an outer scope
var summary = {
    init: function() {
        // access "scrolled"
        scrolled = 0;
    },

    scrollDown: function(e) {
        // access "scrolled"
    },

    scrollUp: function(e) {
        // ...
    }
};

summary.init();

or

var summary = {
    scrolled: 0, // Make it a property of the "summary" object
    init: function() {
        // access "scrolled"
        summary.scrolled = 0;
    },

    scrollDown: function(e) {
        // access "scrolled"
    },

    scrollUp: function(e) {
        // ...
    }
};

summary.init();

Answer 2

Following your question, you should use this.scrolled instead of var. An example would be

 var summary = {
    init: function() {
        this.scrolled = 20;
    },

    scrollDown: function(e) {
        console.log(this.scrolled);
    },

    scrollUp: function(e) {
        console.log(this.scrolled);
    }
 };   
 summary.init();
 summary.scrollDown();

to satisfy your curiosity, you should look up this link How does the “this” keyword work? and Explanation from MDN