Verify Playwright Method Throws

What I do

I perform a deep analysis of a Playwright method's implementation to determine if it can throw an error. This involves tracing execution paths, checking for asynchronous operations (IPC calls), and identifying explicit throw statements or validations.

When to use me

Use this skill when you need to decide whether a Playwright method should be wrapped in an Effect (if it can throw) or mapped 1:1 (if it is guaranteed safe).

Procedure

1. Locate the Implementation

Find the method definition in the Playwright codebase.

• Client-side Logic: context/playwright/packages/playwright-core/src/client/ (e.g., page.ts, locator.ts).
• Protocol Definition: context/playwright/packages/protocol/src/protocol.yml (can help identify commands).

2. Analyze Direct Implementation

Examine the method body.

• Async / Promise-returning:

  • Does it return a Promise?
  • Does it use await?
  • Verdict: Almost always CAN THROW (network errors, timeouts, target closed).

• Synchronous:

  • Does it contain throw new Error(...)?
  • Does it call other methods that might throw synchronously?
  • Does it validate arguments? (e.g., assert(...), checks on options).

3. Trace Deep Calls (The "Deep Check")

If the method calls other internal methods, trace them.

• IPC Calls: Does it call this._channel.send(...) or similar?
  • Verdict: CAN THROW (connection issues, server-side errors).
• Frame/Context Delegation: Does it delegate to this._mainFrame or this._context?
  • Action: Check the implementation of the delegated method in frame.ts or browserContext.ts.
• Utility Functions: Does it call helpers like assertMaxArguments, parseResult, serializeArgument?
  • Verdict: These can throw validation errors.

4. Classify the Method

Based on the analysis, classify the method into one of two categories:

A. Guaranteed Safe (Cannot Throw)

• Criteria:
  • Synchronous.
  • No throw statements.
  • No calls to methods that throw.
  • No IPC / Protocol usage.
  • Pure data access (e.g., returning a private field, creating a wrapper).
• Examples:
  • page.url() (returns a string from local state).
  • page.locator(...) (creates a locator object).
  • page.viewportSize() (returns cached size).
• Result: Map 1:1. Do not wrap in Effect.

B. Can Throw (Unsafe)

• Criteria:
  • Returns a Promise (Async).
  • Performs IPC / Network calls.
  • Contains explicit validation that throws Error.
  • Accesses resources that might be closed/destroyed.
• Examples:
  • page.click(...) (Async, IPC).
  • page.title() (Async, IPC - even if it seems like a property).
  • page.evaluate(...) (Async, script execution).
  • locator.elementHandle() (Async).
• Result: Wrap in Effect<T, PlaywrightError>.

Output Format

When reporting the result of this skill, please provide:

1. Method Name: The method analyzed.
2. File Location: Where the implementation was found.
3. Analysis: Brief explanation of the code path (e.g., "Calls this._channel.click, which is an IPC call").
4. Conclusion: "Can Throw" or "Cannot Throw".

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