Detect Chrome running in headless mode from JavaScript

The user agent string includes HeadlessChrome instead of Chrome. This is probably the signal that you’re intended to look for, so you could use:

/\bHeadlessChrome\//.test(navigator.userAgent)

Other interesting signals include:

• It looks like window.chrome is undefined when headless.
• [innerWidth, innerHeight] is [800, 600] (hardcoded in headless_browser.cc), while [outerWidth, outerHeight] is [0, 0] (which shouldn’t usually happen).