'indexOf' of undefined?

Question

JavaScript

I use this expression:

if ($('div a').attr('data-content').indexOf('warning') + 1) {
    ...

But in the console, the following error occurs:

Uncaught TypeError: Cannot read property 'indexOf' of undefined

HTML:

<div>
    <a data-toggle="popover" data-html="true" title="Блок #1" data-content="Загрузка..."
       role="button" data-placement="bottom"></a>
</div>

When pasted into the data-content attribute, the resulting HTML is:

<div>
    <a data-toggle="popover" data-html="true" title="Блок #1" data-content="<div class="info">info</div><div class="warning">info</div>"
       role="button" data-placement="bottom"></a>
</div>

How to fix it?

Answer 1

I solved the problem with the String function for the inserted string.

Answer 2

1) for data-attributes there is a data() method.
2) Open the console and execute the code
Make sure that it returns. data attributes are case sensitive, e.g.
3) Explain the purpose of this -

<a data-toggle="popover" data-html="true" title="Блок #1" data-content="<div class="info">info</div><div class="warning">info</div>"
       role="button" data-placement="bottom"></a>