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![Alex Hort-Francis](https://uploads.teamtreehouse.com/production/profile-photos/10826830/micro_IMG_20220313_122652_3-1.jpg)
Alex Hort-Francis
17,074 PointsVariable 'headline' not defined, but function still runs! Mysterious..
Hello,
With this code:
const button = document.getElementById('btn-main');
button.addEventListener('click', () => {
headline.style.border = 'solid 2px red';
});
... the headline does indeed get a red border when the 'Update Heading' button is pressed.
However, the variable 'headline' in the Javascript has not been defined!
Typing 'headline' in the console returns the correct h1 element:
<h1 id="headline" style="border: 2px solid red;">My Day</h1>
I can't figure this one out! Does anyone else know?
Is it something to do with browser cache keeping the 'headline' variable maybe?
1 Answer
![Jason Larson](https://uploads.teamtreehouse.com/production/profile-photos/11651180/micro_JLarson-Crop3.jpg)
Jason Larson
8,359 PointsThis works because you are modifying an element that has an id of "headline". It wouldn't work on a class or element, or if the name of the id doesn't conform to standard variable naming (like "btn-main"). Ids are created by default as properties of the global object (in global context). (Please don't ask me where this is documented, as I don't know. I found it googling around for the answer to your question.) Basically, ids act very similar to a global variable. You should avoid this use of them, though, as you could run into issues that are difficult to troubleshoot (like if you had a global variable named "headline", as it would shadow the "headline" property).
Alex Hort-Francis
17,074 PointsAlex Hort-Francis
17,074 PointsWoah, that's crazy! So in effect when the browser renders the HTML into a DOM, it assigns elements with an ID to variables..
I suppose this has something to do with the fact you can navigate a webpage using the ID values in the url..
I just checked and yeah you can reassign the variable 'headline'; I made it into a string ('hello!'). You can even redefine it as a
const
.I wonder if the browser is creating this ID variable as a
var
? Rather thanlet
orconst
.Thanks for your answer, that was very instructive :)
I don't imagine there is much one can do specifically with these ID variables (properties of the global object, like you say), but it's interesting to know that they exist.