how to find shift + key press

HTML

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JavaScript

var shift = false;
document.addEvents({
    'keydown':function(e){
        if (e.code==16) shift =true;
        if (e.code == 57 && shift) alert('(');
        if (e.code == 48 && shift) console.log(')');
    }
    , 'keyup':function(e){
         if (e.code==16) shift=false;   
    }
});