WebView contentSize inspection

WebViewController.m

#import "WebViewViewController.h"
#import <WebKit/WebKit.h>

@interface UIView (AGLayoutExtensions)

- (void)addSubviewWithPinnedEdges:(UIView *)subview;

@end

@implementation UIView (AGLayoutExtensions)

- (void)addSubviewWithPinnedEdges:(UIView *)subview {
    [self addSubview:subview];
    [subview setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self addConstraints:[NSLayoutConstraint
                          constraintsWithVisualFormat:@"H:|-0-[subview]-0-|"
                          options:NSLayoutFormatDirectionLeadingToTrailing
                          metrics:nil
                          views:NSDictionaryOfVariableBindings(subview)]];
    [self addConstraints:[NSLayoutConstraint
                          constraintsWithVisualFormat:@"V:|-0-[subview]-0-|"
                          options:NSLayoutFormatDirectionLeadingToTrailing
                          metrics:nil
                          views:NSDictionaryOfVariableBindings(subview)]];
}

@end

@interface WebViewViewController () <WKNavigationDelegate, WKUIDelegate>

@property (nonatomic, weak) WKWebView *webView;

@end

@implementation WebViewViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    WKWebView *webView = [[WKWebView alloc] initWithFrame:CGRectMake(50.f, 50.f, 500.f, 500.f)];
    webView.navigationDelegate = self;
    webView.UIDelegate = self;
    [self.view addSubviewWithPinnedEdges:webView];
    self.webView = webView;
    
    NSURL *url = [NSURL URLWithString:@"https://www.apple.com"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [self.webView loadRequest:request];
}

- (void)viewDidLayoutSubviews {
    [super viewDidLayoutSubviews];
    [self.webView evaluateJavaScript:@"var body = document.body; var html = document.documentElement; Math.max(body.scrollHeight,body.offsetHeight,html.clientHeight,html.offsetHeight);"
                   completionHandler:^(id _Nullable obj, NSError * _Nullable error) {
                       NSLog(@"viewDidLayoutSubviews");
                       NSLog(@"%@", ((NSNumber *)obj).stringValue); // 735.0
                   }];
}

- (void)webView:(WKWebView *)webView didCommitNavigation:(null_unspecified WKNavigation *)navigation {
    [self.webView evaluateJavaScript:@"var body = document.body; var html = document.documentElement; Math.max(body.scrollHeight,body.offsetHeight,html.clientHeight,html.offsetHeight);"
                   completionHandler:^(id _Nullable obj, NSError * _Nullable error) {
                       NSLog(@"didCommitNavigation");
                       NSLog(@"%@", ((NSNumber *)obj).stringValue); // (null)
                   }];
}

/*! @abstract Invoked when a main frame navigation completes.
 @param webView The web view invoking the delegate method.
 @param navigation The navigation.
 */
- (void)webView:(WKWebView *)webView didFinishNavigation:(null_unspecified WKNavigation *)navigation {
    [self.webView evaluateJavaScript:@"var body = document.body; var html = document.documentElement; Math.max(body.scrollHeight,body.offsetHeight,html.clientHeight,html.offsetHeight);"
                   completionHandler:^(id _Nullable obj, NSError * _Nullable error) {
                       NSLog(@"didFinishNavigation");
                       NSLog(@"%@", ((NSNumber *)obj).stringValue); // 1487.0
                   }];
}

@end

is this something embedded into a Phonegap / Cordova app? or a standalone app (which doesn't show the problem)?