config.js

import {extend, isArray, isObject} from 'vega-util';

export default function(configs) {
  var output = defaults();
  (configs || []).forEach(function(config) {
    var key, value, style;
    if (config) {
      for (key in config) {
        if (key === 'style') {
          style = output.style || (output.style = {});
          for (key in config.style) {
            style[key] = extend(style[key] || {}, config.style[key]);
          }
        } else {
          value = config[key];
          output[key] = isObject(value) && !isArray(value)
            ? extend(isObject(output[key]) ? output[key] : {}, value)
            : value;
        }
      }
    }
  });
  return output;
}

var defaultFont = 'sans-serif',
    defaultSymbolSize = 30,
    defaultStrokeWidth = 2,
    defaultColor = '#4c78a8',
    black = "#000",
    gray = '#888',
    lightGray = '#ddd';

/**
 * Standard configuration defaults for Vega specification parsing.
 * Users can provide their own (sub-)set of these default values
 * by passing in a config object to the top-level parse method.
 */
function defaults() {
  return {
    // default padding around visualization
    padding: 0,

    // default for automatic sizing; options: "none", "pad", "fit"
    // or provide an object (e.g., {"type": "pad", "resize": true})
    autosize: 'pad',

    // default view background color
    // covers the entire view component
    background: null,

    // default event handling configuration
    // preventDefault for view-sourced event types except 'wheel'
    events: {
      defaults: {allow: ['wheel']}
    },

    // defaults for top-level group marks
    // accepts mark properties (fill, stroke, etc)
    // covers the data rectangle within group width/height
    group: null,

    // defaults for basic mark types
    // each subset accepts mark properties (fill, stroke, etc)
    mark: null,
    arc: { fill: defaultColor },
    area: { fill: defaultColor },
    image: null,
    line: {
      stroke: defaultColor,
      strokeWidth: defaultStrokeWidth
    },
    path: { stroke: defaultColor },
    rect: { fill: defaultColor },
    rule: { stroke: black },
    shape: { stroke: defaultColor },
    symbol: {
      fill: defaultColor,
      size: 64
    },
    text: {
      fill: black,
      font: defaultFont,
      fontSize: 11
    },

    // style definitions
    style: {
      // axis & legend labels
      "guide-label": {
        fill: black,
        font: defaultFont,
        fontSize: 10
      },
      // axis & legend titles
      "guide-title": {
        fill: black,
        font: defaultFont,
        fontSize: 11,
        fontWeight: 'bold'
      },
      // headers, including chart title
      "group-title": {
        fill: black,
        font: defaultFont,
        fontSize: 13,
        fontWeight: 'bold'
      },
      // defaults for styled point marks in Vega-Lite
      point: {
        size: defaultSymbolSize,
        strokeWidth: defaultStrokeWidth,
        shape: 'circle'
      },
      circle: {
        size: defaultSymbolSize,
        strokeWidth: defaultStrokeWidth
      },
      square: {
        size: defaultSymbolSize,
        strokeWidth: defaultStrokeWidth,
        shape: 'square'
      },
      // defaults for styled group marks in Vega-Lite
      cell: {
        fill: 'transparent',
        stroke: lightGray
      }
    },

    // defaults for axes
    axis: {
      minExtent: 0,
      maxExtent: 200,
      bandPosition: 0.5,
      domain: true,
      domainWidth: 1,
      domainColor: gray,
      grid: false,
      gridWidth: 1,
      gridColor: lightGray,
      labels: true,
      labelAngle: 0,
      labelLimit: 180,
      labelPadding: 2,
      ticks: true,
      tickColor: gray,
      tickOffset: 0,
      tickRound: true,
      tickSize: 5,
      tickWidth: 1,
      titleAlign: 'center',
      titlePadding: 4
    },

    // correction for centering bias
    axisBand: {
      tickOffset: -1
    },

    // defaults for legends
    legend: {
      orient: 'right',
      offset: 18,
      padding: 0,
      gridAlign: 'each',
      columnPadding: 10,
      rowPadding: 2,
      symbolDirection: 'vertical',
      gradientDirection: 'vertical',
      gradientLength: 200,
      gradientThickness: 16,
      gradientStrokeColor: lightGray,
      gradientStrokeWidth: 0,
      gradientLabelOffset: 2,
      labelAlign: 'left',
      labelBaseline: 'middle',
      labelLimit: 160,
      labelOffset: 4,
      labelOverlap: true,
      symbolType: 'circle',
      symbolSize: 100,
      symbolOffset: 0,
      symbolStrokeWidth: 1.5,
      symbolBaseFillColor: 'transparent',
      symbolBaseStrokeColor: gray,
      titleAlign: 'left',
      titleBaseline: 'top',
      titleLimit: 180,
      titlePadding: 5
    },

    // defaults for group title
    title: {
      orient: 'top',
      anchor: 'middle',
      offset: 4
    },

    // defaults for scale ranges
    range: {
      category: {
        scheme: 'tableau10'
      },
      ordinal: {
        scheme: 'blues',
        extent: [0.2, 1]
      },
      heatmap: {
        scheme: 'viridis'
      },
      ramp: {
        scheme: 'blues',
        extent: [0.2, 1]
      },
      diverging: {
        scheme: 'blueorange'
      },
      symbol: [
        'circle',
        'square',
        'triangle-up',
        'cross',
        'diamond',
        'triangle-right',
        'triangle-down',
        'triangle-left'
      ]
    }
  };
}