Global variable not defined in Javascript

Question

In my case why arr is not defined? I saw the error in jsfiddle's console log. Supposed it's a gobal variable so it can be access in any function scope? http://jsfiddle.net/xgpqe4rv/3/

$(function() {

    autoSlide = setInterval(cycle(), 3000);


    arr = [{
            'logo': 'http://placehold.it/50&text=1'
        },

        {
            'logo': 'http://placehold.it/50&text=2'
        },

        {
            'logo': 'http://placehold.it/50&text=3'
        },

        {
            'logo': 'http://placehold.it/50&text=4'
        }

    ];

    $('img').attr('src', arr[0]['logo']);

    function cycle() {

        var i = 1;

        $('img').attr('src', arr[i]['logo']);

        if (i == 3) {

            i = 0;
        } else {
            i++;

        }
    };

    $('#right').click(function() {
        cycle();
    });
});

@R3tep why? give me a reason

James Lemon
– James Lemon

2015-03-09 15:10:39 +00:00
Commented Mar 9, 2015 at 15:10 — James Lemon
– James Lemon, Commented Mar 9, 2015 at 15:10
autoSlide = setInterval(cycle(), 3000); <--- wrong

epascarello
– epascarello

2015-03-09 15:10:44 +00:00
Commented Mar 9, 2015 at 15:10 — epascarello
– epascarello, Commented Mar 9, 2015 at 15:10

Sterling Archer · Accepted Answer · 2015-03-09 15:11:00Z

1

You're not declaring your variables with var
autoSlide = setInterval(cycle(), 3000); you are passing the return value of the function to the interval, whereas you want a function reference.

autoSlide = setInterval(cycle, 3000);

or

autoSlide = setInterval(function() { cycle() }, 3000);

answered Mar 9, 2015 at 15:11

Sterling Archer

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3 Comments

m59 Over a year ago

Maybe more clear to say that he is passing the return value of the function invocation, which is probably nothing.

James Lemon Over a year ago

oh I see, what a careless mistake I did. But now I'm confused more with variable declaration. I thought without var the variable can be a global var?

m59 Over a year ago

@JamesLemon Yes, it is a global variable, which is exactly why it's wrong. Global variables are bad news. Moreover, global state is bad news.

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