Code using jQuery in Chrome content script fails to work

I'm working on a Chrome extension 开发者_高级运维that injects content into the tumblr 'new posts' page, which has an element with id tag_editor. But I can't get at it using jQuery:

$(document).ready(function() {
    alert($("#tag_editor"));
});

just gives me [object Object], which I assume means that it failed to find an element. If I use document.getElementById instead of $, it works. I have jQuery.js in my manifest.json, so it's not that jQuery isn't loading. What am I doing wrong?

object Object means its returning a jQuery object. You cant alert an object. Try this:

$(document).ready(function() {
    console.log( $("#tag_editor") );
});

Or

$(document).ready(function() {
    alert($("#tag_editor").html());
});

The jQuery function, $(), returns an object; hence your alert message. If you want the underlying DOM object, say:

alert($("#tag_editor")[0]);

or

alert($("#tag_editor").get(0));