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137 lines
3.9 KiB
137 lines
3.9 KiB
/**
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* Set up mock 2D context, for usage in unit tests.
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*
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* Adapted from: https://github.com/Cristy94/canvas-mock
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*/
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var jsdom = require('jsdom');
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var jsdom_global = require('jsdom-global');
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var canvasMock; // Use one canvas instance for all calls to createElement('canvas');
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function replaceCanvasContext (el) {
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el.getContext = function() {
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return {
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fillRect: function() {},
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clearRect: function(){},
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getImageData: function(x, y, w, h) {
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return {
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data: new Array(w*h*4)
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};
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},
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putImageData: function() {},
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createImageData: function(){ return []},
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setTransform: function(){},
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drawImage: function(){},
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save: function(){},
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fillText: function(){},
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restore: function(){},
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beginPath: function(){},
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moveTo: function(){},
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lineTo: function(){},
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closePath: function(){},
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stroke: function(){},
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translate: function(){},
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scale: function(){},
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rotate: function(){},
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arc: function(){},
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fill: function(){},
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//
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// Following added for vis.js unit tests
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//
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measureText: function(text) {
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return {
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width: 12*text.length,
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height: 14
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};
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},
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};
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}
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};
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/**
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* Overrides document.createElement(), in order to supply a custom canvas element.
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*
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* In the canvas element, getContext() is overridden in order to supply a simple
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* mock object for the 2D context. For all other elements, the call functions unchanged.
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*
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* The override is only done if there is no 2D context already present.
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* This allows for normal running in a browser, and for node.js the usage of 'canvas'.
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*
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* @param {object} the current global window object. This can possibly come from module 'jsdom',
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* when running under node.js.
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* @private
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*/
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function overrideCreateElement(window) {
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var d = window.document;
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var f = window.document.createElement;
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// Check if 2D context already present. That happens either when running in a browser,
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// or this is node.js with 'canvas' installed.
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var ctx = d.createElement('canvas').getContext('2d');
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if (ctx !== null && ctx !== undefined) {
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//console.log('2D context is present, no need to override');
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return;
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}
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window.document.createElement = function(param) {
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if (param === 'canvas') {
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if (canvasMock === undefined) {
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canvasMock = f.call(d, 'canvas');
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replaceCanvasContext(canvasMock);
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}
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return canvasMock;
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} else {
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return f.call(d, param);
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}
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};
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}
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/**
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* Initialize the mock, jsdom and jsdom_global for unit test usage.
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*
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* Suppresses a warning from `jsdom` on usage of `getContext()`. A mock definition is added for
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* it, so the message is not relevant.
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*
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* @param {string} [html=''] html definitions which should be added to the jsdom definition
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* @returns {function} function to call in after(), to clean up for `jsdom_global`
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*/
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function mockify(html = '') {
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// Start of message that we want to suppress.
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let msg = 'Error: Not implemented: HTMLCanvasElement.prototype.getContext'
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+ ' (without installing the canvas npm package)';
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// Override default virtual console of jsdom
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const virtualConsole = new jsdom.VirtualConsole();
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// Set up a simple 'mock' console output. Only 'error' needs to be overridden
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let myConsole = {
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error: (msg) => {
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if (msg.indexOf(msg) === 0) {
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//console.error('all is well');
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} else {
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// All other messages pass through
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console.error(msg);
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}
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}
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};
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// Using the global catch instead of specific event handler, because I couldn't get them to work
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virtualConsole.sendTo(myConsole);
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let cleanupFunction = jsdom_global(
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html,
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{ skipWindowCheck: true, virtualConsole: virtualConsole}
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);
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overrideCreateElement(window); // The actual initialization of canvas-mock
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return cleanupFunction;
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}
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module.exports = mockify;
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