title: Bokeh looking in temp files when trying to load new image using CustomJS
body: <p>I am a novice at Bokeh and using CustomJS to define callbacks. I have written a code to make changes to sliders based on the value of other sliders. I now want to change the image displayed when the value of one of the sliders changes. However, when I run this callback, the image does not get displayed and within the console of the bokeh plot, I saw that bokeh is looking for some file in the temp files.</p>
  
  <pre><code>p = figure(title = 'foo', tools = 'pan, save, wheel_zoom,reset,crosshair', x_range = [0,10], y_range = [0,10])
  
  
  slider1 = Slider(start=0, end=15, value=4,step=.1, title="Delta P")
  slider2 = Slider(start=1400, end = 1800, value=1500, step = 10, title = "Mass Flow")
  
  newdelta = 4
  newflow = 1500
  newCV = CV(4+newdelta, 4, 1.3,225.41, 0.9, newflow, 27.3,968) # CV is a function within my code elsewhere
  
  source = ColumnDataSource(data=dict(url=['C:\\Users\\XXX\\test_sample.jpg'])) 
  
  slider3 = Slider(start=-100, end = 2000, value=newCV, step = 1, title = "CV")
  slider3.callback = CustomJS(args=dict(slider3=slider3, source=source), code="""
  
  
                                  if (slider3.value &lt; 0){
                                      source.data.url= "C:\\\\Users\\\\XXX\\\\new_sample.jpg";
                                      console.log(source.data['url']);
                                  };
                                  source.change.emit();
  
                                  """)                          
  
  
  p.image_url('url', source=source, x=2, y=8, w=6, h=6)
  
  
  slider1.callback = CustomJS(args=dict(slider1=slider1,slider2=slider2,slider3=slider3), code="""
                              slider3.value= slider1.value + slider2.value;
  
  
                              """)
  
  slider2.callback = CustomJS(args=dict(slider1=slider1,slider2=slider2,slider3=slider3), code="""
                              slider3.value= slider1.value + slider2.value;
  
                              """)
  
  show(row(column(slider1, slider2,slider3),p))
  </code></pre>
  
  <p>I am not getting any errors in python but when the code is run and I change slider3 value to be less than 0, the console changes the source.data.url value to the new image but the image does not get loaded. Here is the error:</p>
  
  <pre><code>C:1 GET file:///C:/Users/XXX/AppData/Local/Temp/C net::ERR_FILE_NOT_FOUND
  Image (async)
  e @ bokeh-1.0.4.min.js:31
  t._set_data @ bokeh-1.0.4.min.js:31
  t.set_data @ bokeh-1.0.4.min.js:31
  t.set_data @ bokeh-1.0.4.min.js:31
  (anonymous) @ bokeh-1.0.4.min.js:31
  t.emit @ bokeh-1.0.4.min.js:31
  e.emit @ bokeh-1.0.4.min.js:31
  c._setv @ bokeh-1.0.4.min.js:31
  c.setv @ bokeh-1.0.4.min.js:31
  set @ bokeh-1.0.4.min.js:31
  t.compute_indices @ bokeh-1.0.4.min.js:31
  (anonymous) @ bokeh-1.0.4.min.js:31
  t.emit @ bokeh-1.0.4.min.js:31
  e.emit @ bokeh-1.0.4.min.js:31
  eval @ VM29:10
  t.execute @ bokeh-1.0.4.min.js:31
  t @ bokeh-widgets-1.0.4.min.js:31
  (anonymous) @ bokeh-1.0.4.min.js:31
  t._slide @ bokeh-widgets-1.0.4.min.js:31
  (anonymous) @ bokeh-widgets-1.0.4.min.js:31
  (anonymous) @ bokeh-widgets-1.0.4.min.js:32
  (anonymous) @ bokeh-widgets-1.0.4.min.js:32
  R @ bokeh-widgets-1.0.4.min.js:32
  (anonymous) @ bokeh-widgets-1.0.4.min.js:32
  T @ bokeh-widgets-1.0.4.min.js:32
  O @ bokeh-widgets-1.0.4.min.js:32
  e @ bokeh-widgets-1.0.4.min.js:32
  </code></pre>
  
  <p>Could someone please help me understand what is going wrong and how this can be corrected?</p>