title: How to hide a line by default when using a checkbox in Bokeh
body: <p>We can easily make an interactive graph with Bokeh where the user can toggle a line on and off but I haven’t found a way to hide the line by default (i.e before the user checks a checkbox). As an example, the code below kind of works but when the user first load the page, all the lines are on by default even know none of them are active (active=[]). The user must then select any checkbox to make them disappear and then select a given checkbox to display a given line which is clumsy. So how would one hide the lines by default before the user selects one of them?</p>
  
  <pre><code>from bokeh.io import output_file, show
  from bokeh.layouts import row
  from bokeh.plotting import figure
  from bokeh.models import CheckboxGroup, CustomJS
  
  output_file("toggle_lines.html")
  
  
    ### Main plot
    plot = figure()
  
  # Dummy data for testing
    x = list(range(90))
    y0 = [ a**1.5 for a in x]
    y1 = [ a**1.55 for a in x]
    y2 = [ a**1.60 for a in x]
    y3 = [ a**1.65 for a in x]
  
    l0 = plot.line(x, y0, color='red')
    l1 = plot.line(x, y1, color='red')
    l2 = plot.line(x, y2, color='red')
    l3 = plot.line(x, y3, color='red')
  
    checkbox = CheckboxGroup(labels=["l0",  "l1", "l2", "l3"], active=[])
    checkbox.callback = CustomJS(args=dict(l0=l0, l1=l1, l2=l2, l3=l3, checkbox=checkbox),
                               code="""
                                    l0.visible = 0 in checkbox.active;
                                    l1.visible = 1 in checkbox.active;
                                    l2.visible = 2 in checkbox.active;
                                    l3.visible = 2 in checkbox.active;
                                    """)
  layout = row(checkbox, plot)
  show(layout)
  
  
  </code></pre>