I am trying to understand a bit of JavaScript from http://developer.yahoo.com/maps/simple/jspost.html (appended below). I'd appreciate help understanding two things it. The first is the following: <script type="text/javascript"> createForms(); </script> I don't understand the "createForms()". I know it must be JavaScript but I have looked in the index of several references and do not find any such entry in their indices. My online searches got a few hits but nothing helpful. Where can I find some online doc for createForms()? It seems to create a button labeled "View on Y! Maps" but where does that text (i.e. "View on Y! Maps") come from?
The HTML also contains the following JavaScript: document.write("<scr"+"ipt language=javascript src=http://l.yimg.com/us.js.yimg.com/lib/bc/bc_2.0.4.js></scr"+"ipt>");. Why is the concatenation operator, +, being used here? To my naive mind it seems to be unnecessary.
I'll appreciate any help anyone can offer. Thanks, Bob
</head> <body> <script type="text/javascript" src="jspost.js"></script> <h2>Java script POST sample</h2> <p>Clicking this Button executes a POST request (Sorry, does not work in IE)</p> <p>In this sample the RSS feed is hardcoded. To make this sample into a cool application, dynamically generate a feed.</p> <script type="text/javascript"> createForms(); </script>
>I am trying to understand a bit of JavaScript from >http://developer.yahoo.com/maps/simple/jspost.html (appended below). I'd >appreciate help understanding two things it. The first is the following: > <script type="text/javascript"> > createForms(); > </script> > I don't understand the "createForms()". I know it must be JavaScript but > I have looked in the index of several references and do not find any such > entry in their indices. My online searches got a few hits but nothing > helpful. Where can I find some online doc for createForms()? It seems to > create a button labeled "View on Y! Maps" but where does that text (i.e. > "View on Y! Maps") come from?
> The HTML also contains the following JavaScript: > document.write("<scr"+"ipt language=javascript > src=http://l.yimg.com/us.js.yimg.com/lib/bc/bc_2.0.4.js></scr"+"ipt>");. > Why is the concatenation operator, +, being used here? To my naive mind > it seems to be unnecessary.
> I'll appreciate any help anyone can offer. Thanks, Bob
a)The html source also contains a line <script type="text/javascript" src="jspost.js"></script> That is a javascript file. It will be loaded and becomes part of all the javascript on the page. In that file function createForms() will have been declared. (Try viewing the js file.)
b)The only difference between "script" and "scr"+"ipt" that I can think of is to make it harder to find script elements in a file via text search in the source.
On May 9, 1:41 pm, "eBob.com" <eBob....@totallybogus.com> wrote:
> I am trying to understand a bit of JavaScript fromhttp://developer.yahoo.com/maps/simple/jspost.html (appended below). I'd > appreciate help understanding two things it. The first is the following: > <script type="text/javascript"> > createForms(); > </script> > I don't understand the "createForms()".
It is defined as a function in the script file, jspost.js, which is added to the page by the first script element.
[...]
> The HTML also contains the following JavaScript: document.write("<scr"+"ipt > language=javascript > src=http://l.yimg.com/us.js.yimg.com/lib/bc/bc_2.0.4.js></scr"+"ipt>");. > Why is the concatenation operator, +, being used here? To my naive mind it > seems to be unnecessary.
It is, though it might be used to keep the code tidy. However, it seems to have been used above in an attempt to make browsers ignore the script tags within the string literal when parsing the content of the script element (which they must do to find the closing </script> tag)
The example above is erroneous, since the bit that closes the tag is "</", so that is what must be hidden by escaping the forward slash, so it should have been written:
document.write("<script ...>....<\/script>");
Also, the language attribute is deprecated and shouldn't be used, type is required.
It is examples like this that create a low opinion of such sites, even though there are many other exmaples of technical competence. In addition to the errors already mentioned, nothing should be placed after the closing <html> tag.
> The HTML also contains the following JavaScript: > document.write("<scr"+"ipt language=javascript src=http:// > l.yimg.com/us.js.yimg.com/lib/bc/bc_2.0.4.js></scr"+"ipt>");. Why is > the concatenation operator, +, being used here?
It is a mystical incantation chanted in the face of an issue that the author of the page does not understand.
> To my naive mind it seems to be unnecessary.
It is unnecessary (and fails fully address the issue it is aimed at addressing).
When an HTML parser encounters an opening SCRIPT, where the script element had content, it needs to work out where the corresponding closing SCRIPT tag is before it can pass everything in-between into its javascript interpreter. To do that it can do no more than scan the following text for some significant character sequence. In the event that it encounters the character sequence "</script>" it is going to see that as being the closing SCRIPT tag that corresponds with the opening one, regardless of where that character sequence may appear (that is. even if it is inside a javascript string literal the HTML parser will know nothing about that and just look at the character sequence).
This makes the first concatenation obviously pointless, as the HTML parser is only interested in closing tags not opening ones. The second concatenation does have the effect of modifying what may otherwise have been the character sequence "</script>" and so does render the result uninteresting to the HTML parser. However, the concatenation is still unnecessary and adds an avoidable runtime operation because it is possible to disrupt the "</script> character sequence by inserting a backslash character into it (which the javascript interpreter will treat as an escaping character and process out of the string before it finishes compiling the code). That is, employing the character sequence "<\/script>" in the javascript string literal is sufficient to prevent the HTML parser miss-attributing the result as a closing script tag and avoids the runtime concatenation.
In addition, the HTML specification does not require the HTML parser to be looking for the "</script>" character sequence, it actually says that the first occurrence of the character sequence "</" can be taken as terminating the CDATA content of a SCRIPT element. No browsers have been observe to be that strict when handling HTML, but there are not technical grounds for objecting if one was observe to be taking the HTML specification literally in this regard. You will observe that while the second concatenation operation above does disrupt the "</script>" character sequence it does not disrupt the contained "</". Thus though it may address the issue as observed it fails to address the theoretical issue, while using the '<\/script>" sequence as an alternative addresses both (but still leaves all other possible occurrences of mark-up text in javascript string literals needing some attention given it their closing tags). (Note that none of this is relevant in javascript files that are imported with script SRC attributes as they are never exposed to an HTML parser).
