Why does chrome throw "Uncaught Error: NOT_FOUND_ERR: DOM Exception 8" here?

Question

Below is the code for my YWA wrapper

var astr_ywascript = (document.createElement("script").type = "text/javascript").src = "http://d.yimg.com/mi/eu/ywa.js";
document.head.appendChild(astr_ywascript); // <- error on this line

It's run on page load, so it makes no sense that JS can't find the document head tag.

Any ideas?

Thanks

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Opera throws this error on the same line. Uncaught exception: Error: WRONG_ARGUMENTS_ER Firebug says: document.head is undefined [Break On This Error] document.head.appendChild(astr_ywascript);

Answer 1

In the line

(document.createElement("script").type = "text/javascript").src

you are setting the src property of a string. The assignment in parentheses returns the assigned value. You make the same mistake later in the line, ultimately assigning "http://d.yimg.com/mi/eu/ywa.js" to astr_ywascript

Split it out onto separate lines:

var el=document.createElement("script");
el.type="text/javascript"
el.src=...
document.head.appendChild(el);

Raw Javascript rarely behaves in the fluid way one gets used to with jQuery.

You might also want to get the head as follows:

document.getElementsByTagName("head")[0]

Answer 2

I got this error with Backbone.js because I was doing:

$('#backbone').html(@view.render())

Instead of

$('#backbone').html(@view.render().el)

Like I should have done. Still don't really know what this 'el' business is, but I'm sure I'll figure it out soon.