Create plot with plotly.js and the data is provided by the Flask back-end

plotly_js_barchart.html

<!-- 
============================================================
Plotly.js barchart 
============================================================
-->
<div class="row">
<div class="col-lg-4" style="outline:1px solid black;">
    <strong>Day-ahead prices</strong>
    <div id="chart" class="container col-12"></div>
</div>
</div>

<script src='https://cdn.plot.ly/plotly-latest.min.js'></script>
<script type='text/javascript'>
// Getting the data from Flask session
let x = {{session['da_dates']|safe}};
let y = {{session['da_prices']|safe}};

var trace1 = {
    x: x,
    y: y,
    type: 'scatter',
    line: {shape: 'hv'},
    mode: 'lines',
    name: 'Day-ahead prices',
    marker: {
        color: 'Black',
    }
};

var data = [trace1];

var layout = {
    //https://plotly.com/python/reference/layout/yaxis/
    yaxis: {
        showline: false,
        showgrid: true,
        showticklabels:false,
    },
    xaxis: {
        ticklabeloverflow: "allow",
        tickangle: 0,
        dtick: 3,
        tick0: 1,
    },
    plot_bgcolor: "rgba(0,0,0,0)",
    margin: {
        l:5,
        r:30,
        t:20,
        b:30,
    },
    showlegend: false,
    height: 250,
    font: {
        size:10,
    },
    hoverlabel: {
        font: {
            size:10,
        },
    }
};

var config = {
    responsive: true,
    displayModeBar: false,
}

Plotly.newPlot('chart', data, layout, config);
</script>