Javascript : difference two ways declare variable in a function
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I want to create an object. And, in almost code I have read, they often use this style:

    function student(_id, _name, _year){
       this.id = _id;
       this.name = _name;
       this.year = _year;
    }

But, I don't know what the difference with below code :

    function student (id, name, year){
       var id = _id;
       var name = _name;
       var year = _year;
    }

I have tested for example, `alert` properties to screen, and see no difference.

Thanks :)
