Javascript评估问题

Question

I have page A that issues an ajax call and brings in snipped B. This snippet is being added into the DOM and all the scripts in that snipper are eval-ed. In that snippet, I have 2 script tags as such:

<script type="text/javascript">
function doOptions(){
   alert('doOptions');
}
</script>
<script type="text/javascript">
   X = { 
      x : function(x) {
           alert('x');
      }


   }
</script>

Then the JS that is declared in the above script tags is being used on within snippet B as such:

  <button type="button" onclick="doOptions();"> options </button>       
  <button type="button" onclick="X.x();"> XX </button>

Clicking on the XX button work, but clicking on the options button, does not. Both firefox and IE tell me that doOptions is not defined. Why?

Also, what category of Javascript knowledge is this? Meaning, if I want to read more about this, what do I search for, where do I look in the table of contents in a JS book?

Thanks.

Answer 1

This snippet is being added into the DOM and all the scripts in that snipper are eval-ed.

If you are using innerHTML to insert the script , it will not work - the script content will not be parsed. There are methods to get it working with Internet Explorer , but you'll never have a cross browser solution. You should look at returning the data from the AJAX request in a different format (as text, for example) and then creating and appending the script element using DOM functions. For example:

// Create the script element
var script = document.createElement("script");
script.type = "text/javascript";

// Set the source as the location of the ajax service
script.src = "http://path.to/myajaxhandler.php?ajaxopt=2&anotheropt=5";

// Add the script element
document.getElementsByTagName("head")[0].appendChild(script);

Either that or parse out the text content from the script elements returned in the AJAX call, but that gets more complicated because you'll need to use regular expressions (which aren't ideal for parsing HTML, but might be ok if the content returned isn't too complex).

Answer 2

If my guess is right and your problem falls this case, this might be useful. The problem could be due to the reason that the evals are executed in the calling environments context.

I executed the following test:

function test() {
    eval('x={bar:function(){alert("bar");}}');
    eval('function foo(){alert("foo")}')


}
test();
x.bar(); //succeeds
foo(); //fails.

Here the call foo() fails because it is local to the test() function whereas the variable 'x' is a global variable(since 'var' is not specified) hence the call to bar() on x succeeds;

If you want to make 'foo' function available outside,

function test() {
    eval('x={bar:function(){alert("bar");}}');
    eval('foo = function(){alert("foo")}')


}
test();
x.bar();
foo();

Now we are assigning the function to a global variable ('var' not specified). Now you can call foo() function outside.

Hope this helps.