Using JavaScript with WkWebView - error on UserMessageHandler

Question

When sending a message through Javascript to iOS, I encountered this error message that I can't find any information online: "Can only call UserMessageHandler.postMessage on instances of UserMessageHandler".

I am using a webview to render a webpage on iOS.

I tried adding the same script from native code and I was able to receive the message. However, the same script shows the above error if I deploy it on the web site.

let scriptSource = "window.webkit.messageHandlers.jsHandler.postMessage({command: 'command goes here'});"
let userScript = WKUserScript(source: scriptSource, injectionTime: .atDocumentEnd, forMainFrameOnly: true)
userContentController.addUserScript(userScript)

on the web end, I used the following code

key: "onExit",
                    value: function() {
                        var t = function() {
                            try {
                                return window.webkit.messageHandlers.jsHandler.postMessage || null
                            } catch (t) {
                                return null
                            }
                        }();
                        if (t)
                            try {
                                t({
                                    command: "command goes here"
                                }), console.log("window.webkit.messageHandlers.jsHandler.postMessage called successfully")
                            } catch (t) {
                                console.log("error thrown when calling window.webkit.messageHandlers.jsHandler.postMessage - " + (t || {}).message)
                            }
                        else
                            console.log("window.webkit.messageHandlers.jsHandler.postMessage not found!")
                    }

What did you find out?

dazza5000
– dazza5000

2020-08-31 22:31:36 +00:00
Commented Aug 31, 2020 at 22:31 — dazza5000
– dazza5000, Commented Aug 31, 2020 at 22:31

li bobby · Accepted Answer · 2020-11-04 09:44:24Z

3

Explicit bind this will resolve the error:

window.webkit.messageHandlers.jsHandler.postMessage.bind(window.webkit.messageHandlers.jsHandler)

answered Nov 4, 2020 at 9:44

li bobby

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