WebView2 Eval Demo - JavaScript Expression Evaluation

Overview

Demonstrates cWebView2Host's Script.Eval method for synchronously executing JavaScript expressions and getting return values in VB6.

Project Structure

Download Source [ Note: Re-register the DLL file in the bin directory ]

Source code is available in the VBMAN2 project's demos/webview2/eval directory.

eval/
  ├── Form1.frm              # Main form, containing JS evaluation logic
  ├── pic/
  │   └── eval.png           # Screenshot of running result
  ├── vbman2_webview2.vbp    # VB6 project file
  └── vbman2_webview2.vbw    # VB6 workspace file

Core Code Walkthrough

1. Declaration and Initialization (Form1.frm)

Dim wv As New cWebView2Host

Private Sub Form_Load()
    wv.Initialize Me.hWnd, "https://vb6.pro"
End Sub

2. JavaScript Evaluation

Private Sub GetHtml_Click()
    MsgBox wv.Script.Eval("return document.querySelector('.hero-title').innerHTML")
End Sub

Key features of Script.Eval:

• Use return statement in code to return values
• Synchronous execution, directly get return value
• Supports complete JS syntax including DOM operations

Feature Description

1. Script.Eval Method

   • Wraps JS code as a function, then executes it
   • Uses return to return values to VB6
   • Synchronous execution, immediately get results

2. DOM Queries

   • Uses document.querySelector() to select DOM elements
   • Read element attributes (innerHTML, textContent, etc.)

Technical Notes

1. Eval vs JsRun differences:

   • Script.Eval(code) — Wrapped as function, requires return for value
   • JsRun(expression) — Directly executes expression, auto-returns result

2. Must use return: Eval wraps code as function EvalFuncName(){<code>}, so return is needed to pass back values

3. Error handling: If JS code throws an exception, Eval returns an empty string

Use Cases

1. Reading specific element text or attributes from a page
2. Executing complex DOM queries
3. Evaluating JS expressions (e.g., JSON processing, date formatting)

Extension Suggestions

1. Combine Script.Eval and SetData for more flexible data reading
2. For simple property reading, prefer JsProp or JsRun
3. When using Eval for complex multi-line logic, verify in the browser console first