Chartjs-How to constantly update y axis using a C# function to update a Live (Streaming) Chart.js Chart in ASP.NET core Web Application Razor Pages

You can’t do that directly. The code is executed only once when the request is sent to server.

In order to achieve your goals, you need create a server side code snippet to generate data. For example, if you prefer Razor Page, create a OnGetRefresh() handler as below:

public IActionResult OnGetRefresh()
{
    return new JsonResult(this.RNG());
}

private int RNG(){
    Random rnd = new Random();
    int num = rnd.Next(1, 10);
    return num;
}

And then pull data when onRefresh using Ajax or websocket. Here’s a demo that uses Ajax to get the data from server:

function onRefresh(chart) {
    function pushData(yData){
        chart.config.data.datasets.forEach(function(dataset) {
            dataset.data.push({ x: Date.now(), y:yData });
        });
    }
    var xhr = new XMLHttpRequest();
    // you might want to custom the url
    var handlerUrl = '/Index?handler=Refresh';
    xhr.open('GET', handlerUrl , true);  
    xhr.onreadystatechange = function(){
        if (xhr.readyState === XMLHttpRequest.DONE) {
            if (xhr.status == 200) {
                pushData(xhr.responseText);
                return;
            } 
            console.log("error happens: receives a status code ",xhr.status)
        }
    }
    xhr.send();
}

A Working Demo Using your config: