mychart.js

document.getElementById('fx').addEventListener('click', draw);
// tocalculate.innerHTML="4*sin(x)+5*cos(x/2)"
function draw() {

    try {
      // compile the expression once
      const expression = tocalculate.innerHTML;
      const expr = math.compile(expression)

      // evaluate the expression repeatedly for different values of x
      const xValues = math.range(-10, 10, 0.5).toArray()
      const yValues = xValues.map(function (x) {
        return expr.evaluate({x: x})
      })

      // render the plot using plotly
      const trace1 = {
        x: xValues,
        y: yValues,
        type: 'scatter'
      }
      const data = [trace1]
      Plotly.newPlot('plot', data)
    }
    catch (err) {
      console.error(err)
      alert(err)
    }
  }