views.py
context = {'select_company': select_company,}
return render(request, 'invest/chart.html', context)
html
<option value="{{o}}">{{select_company}}</option>----------{{select_company}} can show its value
<script>
company = {{select_company|safe}}; ---------------js tell me undefined
</script>
django 2.2 python 3.7 how to solve the weird problem
Maybe data attributes:
your_template.html
<div id="some-element" data-company="{{ selected_company }}"></div>
your_javascript.js
const element = document.querySelector('#some-element');
console.log(element.dataset.company);
When you want to assign a template variable to a string in javascript, you need to add the quotes. {{ select_company|safe }} will just expand the string in your template so you end up with:
var company = some string;
Since some isn't defined as variable, you get an "undefined" error.
Always do this:
var company = "{{ select_company|safe }}";
which will render as
var company = "some company";
Tip: Always take a look at the rendered source code in your browser developer tools when you get errors in your HTML pages, you will spot these kind of mistakes much easier.
var company = "{{ select_company|safe }}"