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JavaScript JavaScript and the DOM (Retiring) Traversing the DOM Child Traversal

Ciaran McNally
Ciaran McNally
7,052 Points
Posted by Ciaran McNally
Ciaran McNally
7,052 Points

Child Traversal Challange - Appears correctly in preview but fails

My codes seems to work correctly in the preview window but when I click check work I get 'Bummer: Cannot read property '1' of null'

What am I doing wrong?

Thanks

app.js 
var section = document.querySelector('section');
var paragraphs = section.children;

for (var i = 0; i <= paragraphs.length; i++){
  paragraphs[i].style.color = 'blue';
}
index.html 
<!DOCTYPE html>
<html>
    <head>
        <title>Child Traversal</title>
    </head>
    <body>
        <section>
            <p>This is the first paragraph</p>
            <p>This is a slightly longer, second paragraph</p>
            <p>Shorter, last paragraph</p>
        </section>
        <footer>
            <p>&copy; 2019</p> 
        </footer>
        <script src="app.js"></script>
    </body>
</html>

1 Answer

Owen Bell
Owen Bell
8,060 Points
Owen Bell
Owen Bell
8,060 Points

The issue lies in your for loop's termination condition:

i <= paragraphs.length;

Recall that in JavaScript, arrays are zero-indexed - this means that the last element's index is in fact equal to one less than its array's length. As written, your loop will execute for values of i up to and including paragraphs.length. When the loop executes for i = paragraphs.length, It searches for an index that does not exist in the array and returns a null value. As the style property cannot be read for a value of null, the code throws an error.

Your preview appears as expected because the loop will still execute on all the items in the array - it just hits a problem at the end of the loop when it tries to search for an index in excess of the final item.

Owen Bell
Owen Bell
8,060 Points
Owen Bell
Owen Bell
8,060 Points

No problem! Happy to help :)