WebBrowser1控件必须打开一个页面，空白也可以，然后在下列事件处理

Private Sub WebBrowser1_DocumentComplete(ByVal pDisp As Object, URL As Variant)

    Dim doc As Document

    Dim js As ScriptElement

    Set js = doc.createElement("script")

    js.defer = True

    js.src = "http://localhost/a.js"

    doc.body.appendChild js

End Sub