face-api/src/dom/getContext2dOrThrow.ts

import { env } from '../env/index';
import { resolveInput } from './resolveInput';

export function getContext2dOrThrow(canvasArg: string | HTMLCanvasElement | CanvasRenderingContext2D): CanvasRenderingContext2D {
  const { Canvas, CanvasRenderingContext2D } = env.getEnv();
  if (canvasArg instanceof CanvasRenderingContext2D) return canvasArg;
  const canvas = resolveInput(canvasArg);
  if (!(canvas instanceof Canvas)) throw new Error('resolveContext2d - expected canvas to be of instance of Canvas');
  const ctx = canvas.getContext('2d', { willReadFrequently: true });
  if (!ctx) throw new Error('resolveContext2d - canvas 2d context is null');
  return ctx;
}