Method acquireContext

src/platform/platform.dom.js:267–288

* @param {HTMLCanvasElement} canvas * @param {number} [aspectRatio] * @return {CanvasRenderingContext2D|null}

(canvas, aspectRatio)

	 * @return {CanvasRenderingContext2D|null}
	 */
  acquireContext(canvas, aspectRatio) {
    // To prevent canvas fingerprinting, some add-ons undefine the getContext
    // method, for example: https://github.com/kkapsner/CanvasBlocker
    // https://github.com/chartjs/Chart.js/issues/2807
    const context = canvas && canvas.getContext && canvas.getContext('2d');

    // `instanceof HTMLCanvasElement/CanvasRenderingContext2D` fails when the canvas is
    // inside an iframe or when running in a protected environment. We could guess the
    // types from their toString() value but let's keep things flexible and assume it's
    // a sufficient condition if the canvas has a context2D which has canvas as `canvas`.
    // https://github.com/chartjs/Chart.js/issues/3887
    // https://github.com/chartjs/Chart.js/issues/4102
    // https://github.com/chartjs/Chart.js/issues/4152
    if (context && context.canvas === canvas) {
      // Load platform resources on first chart creation, to make it possible to
      // import the library before setting platform options.
      initCanvas(canvas, aspectRatio);
      return context;
    }

    return null;
  }

  /**
	 * @param {CanvasRenderingContext2D} context