有三种实现途径

1. WKScriptMessageHandler

OC部分：注册并实现Handler
将OC中的方法"nativeMethod"注册为JavaScript Message Handler，从而WebView中的JavaScript代码可以调用该方法

// Register in Objective-C code
- (void)setupWKWebView
{
    // [WKWebViewConfiguration alloc]返回一个被分配和初始化的WKWebViewConfiguration对象的指针
    // init方法是WKWebViewConfiguration类的实例方法
    WKWebViewConfiguration *configuration = [[WKWebViewConfiguration alloc] init];
    
    configuration.userContentController = [[WKUserContentController alloc] init];
    
    // 将OC中的方法"nativeMethod"注册为JavaScript Message Handler，从而可以在WebView中执行JavaScript代码时调用该方法
    [configuration.userContentController 
        addScriptMessageHandler:self // addScriptMessageHandler是方法名，self是参数1
        name:@"nativeMethod"]; // name是参数2
    
    // 初始化WKWebView
    WKWebView *webView = 
        [[WKWebView alloc]
            initWithFrame:self.view.frame
            configuration:configuration];
}

// Handler method defined in WKScriptMessageHandler
- (void)userContentController:
    (WKUserContentController *)userContentController //userContentController是参数1
    didReceiveScriptMessage:(WKScriptMessage *)message //message是参数2
{
    if ([message.name isEqualToString:@"nativeMethod"]) // 当JS端调用的是nativeMethod时
    {
        ... //OC端的handler逻辑实现
    }
}

JS部分：调用Handler
调用"nativeMethod"

// Invoke in JavaScript code
window.webkit.messageHandlers.nativeMethod.postMessage();

2. WebViewJavascriptBridge

OC部分：注册并实现Handler
注册名为"nativeMethod"的Handler

// OC中 调用bridgeForWebView:方法，来初始化WebViewJavascriptBridge
// self.bridge将被设置为WKWebView的navigationDelegate属性
self.bridge = [WebViewJavascriptBridge bridgeForWebView:webView];

[self.bridge registerHandler:@"nativeMethod" //参数1，JS端以这个函数名调用该注册的native方法
    handler: //参数2的参数名，冒号后面跟着参数2的参数值，是一个block；当JS端调用nativeMethod方法时，OC端执行该block
    ^(id data, WVJBResponseCallback responseCallback) 
    // ^代表后面是一个block 
    // data是JS端传递过来的数据
    // responseCallback是 OC端的 block 执行完毕之后，往 JS 端传递的数据
    {
        ... // block中的代码，这些代码在JS端调用nativeMethod时被执行
    }
];

JS部分：调用Handler

WebViewJavascriptBridge.callHandler('nativeMethod', data, function(responseData) {
    // 处理来自Objective-C的响应数据
    console.log(response); 
});

例如我们使用Frida分析出来，某app的wkwebview中有如下handler：

{
    callNavigationSelectView = "<__NSMallocBlock__: 0x281d4a440>";
    checkNotificationPermission = "<__NSMallocBlock__: 0x281d4b240>";
    clickControlToShare = "<__NSMallocBlock__: 0x281d4bf00>";
    couponPaySuccess = "<__NSMallocBlock__: 0x281d4a780>";
    doQRScan = "<__NSMallocBlock__: 0x281d4bf80>";
    faceDetect = "<__NSMallocBlock__: 0x281d4bcc0>";
    getDeviceAlipay = "<__NSMallocBlock__: 0x281d4a4c0>";
    getDeviceId = "<__NSMallocBlock__: 0x281d4a800>";
    getDeviceInfo = "<__NSMallocBlock__: 0x281d4a680>";
    getLocation = "<__NSMallocBlock__: 0x281d4a600>";
    getNetworkStatus = "<__NSMallocBlock__: 0x281d4b0c0>";
    getOtherDeviceInfo = "<__NSMallocBlock__: 0x281d4b540>";
    getSMDeviceId = "<__NSMallocBlock__: 0x281d4a2c0>";
    getTripEmail = "<__NSMallocBlock__: 0x281db04c0>";
    getUserInfo = "<__NSMallocBlock__: 0x281d4a540>";
    goToKF = "<__NSMallocBlock__: 0x281d4a340>";
    goToVideoPlayer = "<__NSMallocBlock__: 0x281d4a700>";
    hideLoadingDialog = "<__NSMallocBlock__: 0x281d4b3c0>";
    jdPayHandle = "<__NSMallocBlock__: 0x281d4b900>";
    jumpToMiniPro = "<__NSMallocBlock__: 0x281d4a380>";
    requestNotificationPermission = "<__NSMallocBlock__: 0x281d4af00>";
    saveImage = "<__NSMallocBlock__: 0x281d4a500>";
    sendMsg = "<__NSMallocBlock__: 0x281d4a5c0>";
    shareOnTheWebviewPage = "<__NSMallocBlock__: 0x281d4a640>";
    shareWxImages = "<__NSMallocBlock__: 0x281d4b4c0>";
    shareWxMinipg = "<__NSMallocBlock__: 0x281d4a580>";
    startAuthoritySetting = "<__NSMallocBlock__: 0x281d4a300>";
    startNetworkSetting = "<__NSMallocBlock__: 0x281d4a7c0>";
    statusBarShare = "<__NSMallocBlock__: 0x281d4ad40>";
    uploadTripEmail = "<__NSMallocBlock__: 0x281d49b40>";
    webviewClose = "<__NSMallocBlock__: 0x281d4a740>";
    webviewGoBack = "<__NSMallocBlock__: 0x281d4a480>";
}

这时候在JS端就可以这么调用：

WebViewJavascriptBridge.callHandler('getLocation', function(response) {
  console.log(response); 
});

确实能调用起来

3. DSBridge

这个不是很常见

OC部分：

@implementation JsObject
- (NSString *) nativeMethod:(NSString *) msg
{
    ...
}
@end

DWKWebView* dwebview = [[DWKWebView alloc] initWithFrame:bounds];
[dwebview addJavascriptObject:[[JsObject alloc] init] namespace:nil];

JS部分：

var dsBridge=require("dsbridge");
var str=dsBridge.call("nativeMethod","arg");

参考：
Medusa Attack: Exploring Security Hazards of {In-App}{QR} Code Scanning[C]//32nd USENIX Security Symposium (USENIX Security 23). 2023: 4607-4624.