JSFiddle - React, Tailwind, and code Playground

HTML

<div id="table_div">
    <table border="1">
        <tr><td>Value 1</td><td>2</td></tr>
        <tr><td>Value 2</td><td>3</td></tr>
        <tr><td>Value 3</td><td>10</td></tr>
    </table>
</div>
<div id="log"></div>

JavaScript

var tableEl = document.getElementById("table_div").getElementsByTagName("table")[0];
var rowsEl = tableEl.getElementsByTagName("tr");
var chartDatasetData = [];
for ( var r = 0; r < rowsEl.length; r++ ){
    //log("in row " + r);
    var columnsEl = rowsEl[r].getElementsByTagName("td");
    for ( var c = 0; c < columnsEl.length; c++ ){
        //log("in col " + r);
        if(c > 0){
            var columnData = chartDatasetData[c-1];
            if( columnData == undefined ){
                chartDatasetData[c-1] = [];
            }
            var columnRowData = chartDatasetData[c-1][r];
            if( columnRowData == undefined ){
                chartDatasetData[c-1][r] = [];
            }
            var iValue = parseInt(columnsEl[c].innerHTML);
            log("pushing value " + iValue + " to " + (c-1) + "," + r);
            chartDatasetData[c-1][r].push(iValue);
        }
    }
}
var newData = [];
for (var j=0; j<chartDatasetData[0].length; j++){
    //data has to be casted to int again!!
    newData.push(parseInt(chartDatasetData[0][j]));
    // this will not work
    //newData.push(chartDatasetData[0][j]);
}

var upperValue2 = Number.MIN_VALUE;
var lowerValue2 = Number.MAX_VALUE;
for (var j=0; j<newData.length; j++){
    log(newData[j] + ">" + upperValue2 + " = " + (newData[j] > upperValue2));
    if ( newData[j] > upperValue2) { 
        upperValue2 = newData[j] 
    };
    log(newData[j] + "<" + lowerValue2 + " = " + (newData[j] < lowerValue2));
    if ( newData[j] < lowerValue2) { 
        lowerValue2 = newData[j] 
    };
}
log("Table-Values: min " + lowerValue2 + ", max " + upperValue2);

function log(msg){
    document.getElementById("log").innerHTML = document.getElementById("log").innerHTML + msg + "<br/>";
}