如何基于JavaScript变量修改Swift变量？（JS变量传递至Swift）

Got it, let's get this working for you! The core issue with your current code is that you're only running JavaScript to fetch the element, but not sending back a result that Swift can use to update your checkElement variable. Here's how to fix it:

var checkElement = false

webView.evaluateJavaScript("document.getElementById('element') !== null") { (value, error) in
    if let err = error {
        print("JS evaluation error: \(err)")
        return
    }
    
    // Safely convert the JS result to a Swift boolean and update our variable
    if let elementExists = value as? Bool {
        checkElement = elementExists
        // Optional: Log or act on the updated value right away
        print("Element exists? \(checkElement)")
    }
}

Quick breakdown of what's changed: #

• Instead of just grabbing the element in JS, we directly return a boolean check: "document.getElementById('element') !== null" will send back true if the element exists, false if it doesn't.
• In the completion closure, we cast the returned value (from JavaScript) to a Swift Bool—this is the key link between JS and your Swift variable.
• We then assign that boolean to checkElement to update its value based on the DOM check.

A couple of quick notes to avoid gotchas:

• Make sure your webView is fully loaded (the page has finished rendering) before calling this, otherwise the element might not exist yet even if it's in the HTML.
• If checkElement is a property on a class, add [weak self] to the closure to prevent retain cycles:

webView.evaluateJavaScript("document.getElementById('element') !== null") { [weak self] (value, error) in
    guard let self = self else { return }
    // ... rest of the code ...
    self.checkElement = elementExists
}

内容的提问来源于stack exchange，提问作者Dante