Accordion has a default active panel, but it won't open - vue.js

Question

I am using a frontend library called Element UI to create some accordions on my website. I got an array of objects that I like to create accordions for. FYI, from the element ui website: the v-model used on the accordion specifies the currently active panel. The name attribute is the unique identification of the panel. That means I can do:
<el-collapse v-model="activeName" accordion>
<el-collapse-item title="Consistency" name="1">
<div>content content content</div>
</el-collapse-item>
<el-collapse-item title="Consistency" name="2">
<div>more content more content more content</div>
</el-collapse-item>
</el-collapse>
One this loads, the first accordion will open since in the data object, activeName is set to 1:
data() {
return {
activeName: '1',
}
}
Now I thought I'd just loop through the array and create accordions for the items in my array, and binding the name attribute to the index + 1, so that the first item will have the name attribute equal to 1, the second to 2 etc. So:
<el-collapse v-model="activeName" accordion>
<el-collapse-item
v-for="(item, index) in experience"
:title="item.company"
:name="index + 1"
:key="index"
>
<div> content content content </div>
</el-collapse-item>
</el-collapse>
But for some reason, when the page loads, the first item in the accordion won't open automatically. They're all closed by default. I created a codesandbox with the problem that you can see for yourself here: codesandbox

Answer 1

The problem is that when you run a for loop and assign name, it's a number and not a string.
:name="index+1" <---- This is a number
But, activeName is a string. So, the values don't match and that's why the accordian does not open on page load.
Here's an updated sandbox: https://codesandbox.io/s/vue-template-ysm79
I changed activeName to a number. The for loop accordian will now open and the normal HTML accordians won't.