How can I access the function which inside different js file in JQUERY?

How can I access the function which inside different js file in JQUERY?

And here is the struct of the HTML as below: 

$(function () {    
    function WhiteNav() {
        $("#LOGO>img").attr('src', '/images/LOGOWhite.svg');
        $("#NavUL a").css("color", "#cecece");
    }    
});

And here is the struct of the HTML as below: 


However, after the browser(Chrome) ran the WhiteNav function in the script, it reported this error and the WhiteNav failed: 


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