0👍
Finally I solve the problem with following codes:
{% for emp_day_output in emp_day_outputs %}
new Date("{{ emp_day_output.output_date|date:"Y-m-d" }}").toLocaleDateString(),
{% endfor %}
With the new Date().toLocaleDateString() function, it makes the html with javascript convert the date string for displaying the chart axis provided by the chart.js.
Source:stackexchange.com