set setBackground config option in setPlotContext

- instead of in `plot_config.js` declaration

Author: etpinard

src/plot_api/plot_api.js

@@ -25,6 +25,7 @@ var Polar = require('../plots/polar');
 var initInteractions = require('../plots/cartesian/graph_interact');
 
 var Drawing = require('../components/drawing');
+var Color = require('../components/color');
 var ErrorBars = require('../components/errorbars');
 var xmlnsNamespaces = require('../constants/xmlns_namespaces');
 var svgTextUtils = require('../lib/svg_text_utils');
@@ -390,10 +391,17 @@ Plotly.plot = function(gd, data, layout, config) {
     });
 };
 
+function setBackground(gd, bgColor) {
+    try {
+        gd._fullLayout._paper.style('background', bgColor);
+    } catch(e) {
+        Lib.error(e);
+    }
+}
 
 function opaqueSetBackground(gd, bgColor) {
     gd._fullLayout._paperdiv.style('background', 'white');
-    Plotly.defaultConfig.setBackground(gd, bgColor);
+    setBackground(gd, bgColor);
 }
 
 function setPlotContext(gd, config) {
@@ -460,6 +468,11 @@ function setPlotContext(gd, config) {
     if(context.displayModeBar === 'hover' && !hasHover) {
         context.displayModeBar = true;
     }
+
+    // default and fallback for setBackground
+    if(context.setBackground === 'transparent' || typeof context.setBackground !== 'function') {
+        context.setBackground = setBackground;
+    }
 }
 
 function plotPolar(gd, data, layout) {

src/plot_api/plot_config.js

@@ -8,8 +8,6 @@
 
 'use strict';
 
-/* eslint-disable no-console */
-
 /**
  * This will be transferred over to gd and overridden by
  * config args to Plotly.plot.
@@ -109,8 +107,9 @@ module.exports = {
     plotGlPixelRatio: 2,
 
     // function to add the background color to a different container
-    // or 'opaque' to ensure there's white behind it
-    setBackground: defaultSetBackground,
+    // or 'opaque' to ensure there's white behind it,
+    // or any other custom function of gd
+    setBackground: 'transparent',
 
     // URL to topojson files used in geo charts
     topojsonURL: 'https://cdn.plot.ly/',
@@ -128,16 +127,3 @@ module.exports = {
     // specification needed
     globalTransforms: []
 };
-
-// where and how the background gets set can be overridden by context
-// so we define the default (plotly.js) behavior here
-function defaultSetBackground(gd, bgColor) {
-    try {
-        gd._fullLayout._paper.style('background', bgColor);
-    }
-    catch(e) {
-        if(module.exports.logging > 0) {
-            console.error(e);
-        }
-    }
-}