JamieMason/get-new-execution-context.md

## get-new-execution-context.md

      
    Raw
  

              get-new-execution-context.md
            
          
    Create a new JavaScript execution context

Source

const getNewExecutionContext = markup =>
  new Promise(resolve => {
    const iframe = document.createElement('iframe');
    iframe.style.display = 'none';
    iframe.setAttribute('src', 'about:blank');

    const intervalID = window.setInterval(() => {
      const context = iframe.contentDocument || iframe.contentWindow.document;
      if (context.readyState === 'complete') {
        clearInterval(intervalID);
        context.defaultView.document.write(markup);
        resolve({
          window: context.defaultView,
          destroy() {
            document.documentElement.removeChild(iframe);
          },
        });
      }
    }, 5);
    document.documentElement.appendChild(iframe);
  });
Example Usage

test('renders a valid doctype', async () => {
  const markup = renderHtmlString();
  const context = await getNewExecutionContext(markup);
  expect(context.window.doctype).toEqual('<!DOCTYPE html>');
  context.destroy();
});