React-ing to the need for a modern MapGuide viewer (Part 17): Reason number 5537485 why react was the right choice

An issue cropped up where the legend was not properly rendering a given layer that has multiple geometry styles. This issue was easily reproducible with the Redline widget.

We were expecting to see this after creating a redline layer and drawing some objects.

But we got this instead

Because this legend is a react component, we can inspect it (and the problem layer node) with the React developer tools

Remember the important React motto: The UI is a function of props and state. The HTML content of the LayerNode should be reflective of the props and state given to it. We should've seen something that resembled 3 style icons. But nothing's there.

So let's just check that the layer model for this LayerNode component is indeed a layer with multiple geometry styles

Indeed it is, so that means that the LayerNode component is the culprit. It is not handling the case of multiple geometry styles properly.

As we've already set up our test infrastructure to make it easy to write and run tests, it should be easy to write up an enzyme unit test that shows what we were actually expecting to see when a LayerNode renders a layer that has multiple geometry styles

component.legend.spec.tsx

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import * as React from "react"; import { shallow, mount, render } from "enzyme"; import { MapLayer } from "../src/api/contracts/runtime-map"; import { LayerNode } from "../src/components/legend"; import { ILegendContext } from "../src/components/context"; // Mocks the ILegendContext needed by LayerNode and other legend sub-components function mockContext(): ILegendContext { return { getIconMimeType: () => "image/png", getStdIcon: (path: string) => path, getChildren: (id) => [], getCurrentScale: () => this.props.currentScale, getTree: () => {}, getGroupVisibility: (group) => group.ActuallyVisible, getLayerVisibility: (layer) => layer.ActuallyVisible, setGroupVisibility: () => {}, setLayerVisibility: () => {}, getLayerSelectability: (layer) => true, setLayerSelectability: () => {}, getGroupExpanded: (group) => true, setGroupExpanded: () => {}, getLayerExpanded: (layer) => true, setLayerExpanded: () => {} }; } describe("components/legend", () => { it("renders a multi-geom-style layer with a rule for each geom style", () => { const layer: MapLayer = { Type: 1, Selectable: true, LayerDefinition: "Session:841258e8-63f9-11e7-8000-0a002700000f_en_MTI3LjAuMC4x0AFC0AFB0AFA//testing.LayerDefinition", Name: "_testing", LegendLabel: "testing", ObjectId: "abcd12345", DisplayInLegend: true, ExpandInLegend: true, Visible: true, ActuallyVisible: true, ScaleRange: [ { MinScale: 0, MaxScale: 10000, FeatureStyle: [ { Type: 4, Rule: [ { Icon: "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAABHNCSVQICAgIfAhkiAAAAB1JREFUOI1j/M/A8J+BAsBEieZRA0YNGDVgMBkAAFhtAh6Zl924AAAAAElFTkSuQmCC" } ] }, { Type: 4, Rule: [ { Icon: "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAABHNCSVQICAgIfAhkiAAAACVJREFUOI1jYBgFwwAwMjD8bcAjL8rAwKCNR56LibruGQVDFAAACkEBy4yPOpAAAAAASUVORK5CYII=" } ] }, { Type: 4, Rule: [ { Icon: "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAABHNCSVQICAgIfAhkiAAAAFhJREFUOI3t0D0OQFAUROHPIwoNS7ZJe5BoKJR+OpVH4jUkTjv3TDI3w6Z2zooNeSSfKNQYIwd3NISH6sFfQLCkFmQJdkVIGlG+44mfLyjMaCPpgO7C7tkBAXgKXzBhmUQAAAAASUVORK5CYII=" } ] } ] } ] }; const wrapper = shallow(<LayerNode layer={layer} />, { context: mockContext() }); const rules = wrapper.find("RuleNode"); expect(rules.length).toBe(3); //One for each geom style }); });

Running this in jest confirms our expectations were not met:

Summary of all failing tests
 FAIL  test\component.legend.spec.tsx (6.75s)
  ● components/legend › renders a multi-geom-style layer with a rule for each geom style

    expect(received).toBe(expected)

    Expected value to be (using ===):
      3
    Received:
      0

      at Object. (test/component.legend.spec.tsx:149:30)
      at Promise.resolve.then.el (node_modules/p-map/index.js:42:16)
      at process._tickCallback (internal/process/next_tick.js:103:7)


Test Suites: 1 failed, 22 passed, 23 total
Tests:       1 failed, 94 passed, 95 total
Snapshots:   0 total
Time:        14.532s
Ran all test suites.

We expected 3 RuleNode components (one for each geometry style) to have been rendered, but we only got nothing.

A look at the LayerNode rendering shows why. It only considered the first feature style of any layer's scale range.

So once that was fixed, not only does our test pass, but we have visual confirmation that multi-geometry-style layers now render like they did in the Fusion and AJAX viewers.

So the reason for writing this post was just a re-affirmation of my choice for using React to build this viewer.

• The top-quality developer/debugging experience.
• The react way of thinking about UIs that allowed me to easily identify the culprit (the LayerNode component)
• The top-quality testing ecosystem around React (Jest, enzyme) that allowed me to easily write a unit test on this component to confirm and verify my expectations