Determine if user navigated from mobile Safari

best practice is:

function isMobileSafari() {
    return navigator.userAgent.match(/(iPod|iPhone|iPad)/) && navigator.userAgent.match(/AppleWebKit/)
}

UPDATE: This is a very old answer and I cannot delete it because the answer is accepted. Check unwitting's answer below for a better solution.

---

You should be able to check for the "iPad" or "iPhone" substring in the user agent string:

var userAgent = window.navigator.userAgent;

if (userAgent.match(/iPad/i) || userAgent.match(/iPhone/i)) {
   // iPad or iPhone
}
else {
   // Anything else
}

Merged all the answers and comments. This is the result.

function iOSSafari(userAgent) {
    return /iP(ad|od|hone)/i.test(userAgent) &&
      /WebKit/i.test(userAgent) &&
      !(/(CriOS|FxiOS|OPiOS|mercury)/i.test(userAgent));
}


// Usage:
// if iOSSafari(window.navigator.userAgent) { /* iOS Safari code here */ }

// Testing:
var iPhoneSafari = [
  "Mozilla/5.0 (iPhone; CPU iPhone OS 14_4_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/14.0.3 Mobile/15E148 Safari/604.1",
  "Mozilla/5.0 (Apple-iPhone7C2/1202.466; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543 Safari/419.3",
  "Mozilla/5.0 (iPhone; CPU iPhone OS 11_0 like Mac OS X) AppleWebKit/604.1.34 (KHTML, like Gecko) Version/11.0 Mobile/15A5341f Safari/604.1",
  "Mozilla/5.0 (iPhone; CPU iPhone OS 11_0 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) Version/11.0 Mobile/15A372 Safari/604.1",
  "Mozilla/5.0 (iPhone; CPU iPhone OS 11_0 like Mac OS X) AppleWebKit/604.1.38 (KHTML, like Gecko) Version/11.0 Mobile/15A5370a Safari/604.1",
  "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) Version/12.0 Mobile/15E148 Safari/604.1",
  "Mozilla/5.0 (iPhone9,3; U; CPU iPhone OS 10_0_1 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) Version/10.0 Mobile/14A403 Safari/602.1",
  "Mozilla/5.0 (iPhone9,4; U; CPU iPhone OS 10_0_1 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) Version/10.0 Mobile/14A403 Safari/602.1",
];
console.log("All true:", iPhoneSafari.map(iOSSafari));

var iPhoneNotSafari = [
  "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/69.0.3497.105 Mobile/15E148 Safari/605.1",
  "Mozilla/5.0 (iPhone; CPU iPhone OS 12_0 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) FxiOS/13.2b11866 Mobile/16A366 Safari/605.1.15",
];
console.log("All false:", iPhoneNotSafari.map(iOSSafari));

See https://developer.chrome.com/multidevice/user-agent#chrome_for_ios_user_agent - the user agent strings for Safari on iOS and for Chrome on iOS are inconveniently similar:

Chrome

Mozilla/5.0 (iPhone; U; CPU iPhone OS 5_1_1 like Mac OS X; en) AppleWebKit/534.46.0 (KHTML, like Gecko) CriOS/19.0.1084.60 Mobile/9B206 Safari/7534.48.3

Safari

Mozilla/5.0 (iPhone; U; CPU like Mac OS X; en) AppleWebKit/420+ (KHTML, like Gecko) Version/3.0 Mobile/1A543 Safari/419.3

Looks like the best approach here is to first of all check for iOS as other answers have suggested and then filter on the stuff that makes the Safari UA unique, which I would suggest is best accomplished with "is AppleWebKit and is not CriOS":

var ua = window.navigator.userAgent;
var iOS = !!ua.match(/iPad/i) || !!ua.match(/iPhone/i);
var webkit = !!ua.match(/WebKit/i);
var iOSSafari = iOS && webkit && !ua.match(/CriOS/i);