detect-prerendering.md

Detect request from Prerendering engine during runtime

Prerendering engine will set window.IS_PRERENDERING global variable to true. Detecting request from prerendering engine might be as easy as:

if (window.IS_PRERENDERING) {
  // This request is coming from Prerendering engine
}

Note: window.IS_PRERENDERING might be undefined on initial page load, and may change during runtime. That's why we recommend to pre-define a setter for IS_PRERENDERING:

let _is_prerendering = false;
Object.defineProperty(window, 'IS_PRERENDERING', {
  set(val) {
    _is_prerendering = val;
    if (_is_prerendering === true) {
      // This request is coming from Prerendering engine
    }
  },
  get() {
    return _is_prerendering;
  }
});