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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Empty function
Supersedes: <2789227.5fSG56mABF@PointedEars.de>
Date: Sun, 08 Jan 2017 23:40:38 +0100
Organization: PointedEars Software (PES)
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Xref: csiph.com comp.lang.javascript:32143

Andrew Poulos wrote:

> […] Here is the complete code
> 
> var Drag = {
>    obj: null,
>    init: function(o, posX, posY, minX, minY) {
>      if (!o) return;
>      o.onmousedown = Drag.start;
>      o.root = o;
>      o.root.style.left = posX + "px";
>      o.root.style.top = posY + "px";
>      o.minX = minX;
>      o.minY = minY;
>      o.root.onDragStart = function() {};
>      o.root.onDragEnd = function() {};
>      o.root.onDrag = function() {};

As indicated by “o.root.style”, “o.root” appears to store a reference to a 
DOM element object.  In that case, the latter three lines are error-prone:

They would only work in the MSHTML DOM before version 9 and any DOM 
compatible to it.  In addition, the names of the standard event-handler 
properties are all-lowercase; so in a W3C DOM implementation the referred 
object does not have those properties.  It is a host object, and assigning 
to potentially non-existing property of a host object, thereby attempting
to augment it with properties, is a recipe for disaster.

Since DOM element objects usually do not have “minX” and “minY” properties, 
the latter possibility is more likely.

>    },
>    start: function(e) {
>      e = e || window.event;
>      var o = Drag.obj = this,
>          y = parseInt(o.root.style.top, 10),
>          x = parseInt(o.root.style.left, 10);
>      o.root.onDragStart(x, y);

Given the augmented code, this line suggests that the author attempted to 
augment a host object (see above), and that they have no clue how to 
properly dispatch an event to such an object.

-- 
PointedEars
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