feat: support access iframe

[fatelei]

fix #50

getFrame(): Frame {
    if (this.activeFrame) {
      return this.activeFrame;  // iframe
    }
    return this.getPage().mainFrame();
  }

browser.getLocator(selector) → getFrame() → activeFrame || mainFrame

[vercel]

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[vercel]

Additional Suggestions:

1. getLocator method uses this.getPage() instead of this.getFrame(), breaking iframe support for regular selectors while refs work correctly

2. handleScreenshot bypasses browser.getLocator() and uses page.locator() directly, losing iframe context and ref support

3. handleSetValue and handleDispatch use page.locator() directly instead of browser.getLocator(), bypassing iframe support and ref support

4. handleBoundingBox uses page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

5. handleInnerText and handleInnerHtml use page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

6. handleCount uses page.locator(command.selector) directly instead of browser.getLocator(), bypassing iframe and ref support

7. handleHighlight uses page.locator(command.selector) directly instead of browser.getLocator(), bypassing iframe support and ref support

8. handleContent uses page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

9. handleClear uses page.locator() directly instead of browser.getLocator(), bypassing iframe support and ref support

10. handleSelectAll uses page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

11. handleScrollIntoView uses page.locator() directly instead of browser.getLocator(), bypassing ref support

12. handleMultiSelect uses page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

13. handleScroll uses page.locator(command.selector) directly instead of browser.getLocator(), bypassing iframe support and ref support

14. handleWheel uses page.locator() directly instead of browser.getLocator(), bypassing iframe and ref support

15. handleInnerHtml and handleInnerText use page.locator() directly instead of browser.getLocator(), bypassing iframe support and ref resolution

16. handleNth function bypasses iframe and ref support by using page.locator() directly instead of browser.getLocator()

17. handleDispatch uses page.locator() directly instead of browser.getLocator(), bypassing iframe support and ref support

[vercel]

Additional Suggestions:

1. handleWait uses page.waitForSelector() directly instead of browser.getLocator().waitFor(), breaking consistency with other handlers and losing support for ref-based selectors and iframe context.

2. handlePress uses page.press() directly instead of browser.getLocator() when a selector is provided, breaking support for iframe context and ref-based selectors

3. handleTap uses page.tap() directly instead of browser.getLocator(), missing support for iframe context and ref-based selectors