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From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Dynamically assign image map values?
Date: Thu, 30 Oct 2014 19:46:04 +0100
Organization: PointedEars Software (PES)
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Jukka K. Korpela wrote:

> 2014-10-30 19:35, Tuxedo wrote:
>> x1 = 100; y1 = 100; x2 = 300; y2 =300;
>>
>> area.setAttribute("coords","+x1+","+y1+","+x2+","+y2+");
>>
>> But this is wrong.
> 
> Yes, because only the second argument matters here, the rest are
> discarded. You need this:
> 
> area.setAttribute("coords", x1 + "," + y1 + "," + x2 + "," + y2);

This and all other setAttribute() calls should be replaced with the 
corresponding form of

  area.coords = x1 + "," + y1 + "," + x2 + "," + y2;

(Likewise, getAttribute() calls should be replaced by property-read access 
unless the original markup attribute value is wanted.) [1]
 
Another possibility here is

  area.coords = [x1, y1, x2, y2];

or (probably safer)

  area.coords = [x1, y1, x2, y2].toString();

    or 

  area.coords = [x1, y1, x2, y2].join();

    or (explicit)

  area.coords = [x1, y1, x2, y2].join(",");

The first form should work (untested in recent environments, but supported 
by previous experience) because the type of the “coords” property should be 
String, as it is an implementation of an interface attribute whose type is 
DOMString; so a built-in setter of that property should convert the value 
RHS to String.  Then the following applies:

The string representation of an Array instance is the comma-separated list 
of the string representation of its elements as returned by 
Array.prototype.toString().  The string representation of String values is 
their value; the string representation of Number values is the one that most 
closely represents the nearest IEEE-754 “double precision” floating-point 
value, in the simplest case the concatenated decimal digits.

As for the second one, the toString() method inherited by Array instances 
returns the same as the inherited join() method when called without 
argument.  Array.prototype.join() without argument (with argument 
“undefined”) defaults to a comma (“,”) as separator. [2]  This is “probably 
safer” than the former approach because it does not rely on a type-
converting setter LHS.

_________
[1] <http://www.w3.org/TR/2014/REC-html5-20141028/embedded-content-0.html#the-area-element>
    (sic!)

[2] <http://ecma-international.org/ecma-262/5.1/#sec-15.4.4.2> pp.
-- 
PointedEars
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