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  1. #1
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    Book: Simply Javascript 2007 - page 135 - this and event

    on page 135 there is the following excerpt from tooltips.js:

    Code:
      showTipListener: function(event)
      {
        Tooltips.showTip(this);
        Core.preventDefault(event);
      },
      
      hideTipListener: function(event)
      {
        Tooltips.hideTip(this);
      }
    1. why is showTip using "this" but preventDefault using "event" ?

    2. why is hideTip using "this" when "event" is the parameter?

    i know it's right under my nose but i'm not quite getting it

    many thanks

  2. #2
    Gre aus'm Pott gold trophysilver trophybronze trophy
    Pullo's Avatar
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    Hi there,

    1.
    In showTipListener this refers to the element on the page which triggered the event, so in this case an anchor element.
    Whereas event is a MouseEvent, who's default action needs preventing.

    2.
    this is available within the scope of the function, without having to pass it explicitly as a parameter.
    You could also write:

    Code JavaScript:
    hideTipListener: function()
    {
      Tooltips.hideTip(this);
    }

    and leave out the event entirely.

  3. #3
    SitePoint Enthusiast
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    ah, thanks, getting clearer, will re-read this section but much better

    this is available within the scope of the function
    i remember reading about 'this' and scope within and outside of a function, will re-read this section of the book

    thanks


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