Unable to invoke JavaScript function in local HTML file with webView.evaluateJavaScript("functionCall()") in SwiftUI XCode preview

Question

I would like to run some JavaScript code on new data each second, which I want to transmit from the iOS side to the web view side.

Let's say I wanted to change the color of the web view back ground once every second. I have code looking somewhat like this:

HTML (htmlDocFileName):

<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8" />
  </head>
  <body style="background-color:#EDF2F7;">
    <script>
        function changeBackgroundColor(colorText) {
            document.body.style.background = colorText;
        }
    </script>
  </body>
</html>

Swift view:

import SwiftUI

struct View: View {
var body: some View {
        RepresentedView()
    }
}

Swift represented view:

import UIKit
import SwiftUI
import WebKit

struct RepresentedView: UIViewRepresentable {
    typealias UIViewType = WKWebView
    
    func makeUIView(context: Context) -> WKWebView {
        let webView = WKWebView()
        let url = url = Bundle.main.url(forResource: "htmlDocFileName", withExtension: "html")!
        webView.loadFileURL(url, allowingReadAccessTo: url)
    }
    func updateUIView(_ uiView: WKWebView, context: Context) {
        uiView.evaluateJavaScript("changeBackgroundColor('red')", completionHandler: nil)
    }
}

When I run the code the web view is presented, but the JavaScript function is not executed.

I am able to evaluate JavaScript by using a WKUserScript instead, but with this method I am unable to run the JavaScript function more than once, which is what I want to do.

I have only tested this in Xcode's preview mode, as I am unable to test a running app container.

humleflue · Accepted Answer · 2022-02-04 19:16:22Z

1

The problem is with the preview. The preview in Xcode is unable to run the JavaScript provided to the evaluateJavaScript() method.

The above code should work in a running app on a device or in a simulator.

edited Feb 4, 2022 at 19:16

answered Feb 4, 2022 at 14:33

humleflue

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