import type * as playwright from 'playwright';
import { z } from 'zod';
import { expectationSchema } from '../schemas/expectation.js';
import { elementSelectorSchema } from '../types/selectors.js';
import { quote } from '../utils/codegen.js';
import { defineTabTool } from './tool.js';
import { generateLocator } from './utils.js';
// Enhanced selector schema for browser tools
const selectorsSchema = z
.array(elementSelectorSchema)
.min(1)
.max(5)
.describe(
'Array of element selectors (max 5) supporting ref, role, CSS, or text-based selection'
);
const evaluateSchema = z.object({
function: z
.string()
.describe('JS function: () => {...} or (element) => {...}'),
selectors: selectorsSchema
.optional()
.describe(
'Optional element selectors. If provided, function receives element as parameter'
),
expectation: expectationSchema.describe(
'Page state config. false for data extraction, true for DOM changes'
),
});
const evaluate = defineTabTool({
capability: 'core',
schema: {
name: 'browser_evaluate',
title: 'Evaluate JavaScript',
description:
'Evaluate JavaScript expression on page or element and return result',
inputSchema: evaluateSchema,
type: 'destructive',
},
handle: async (tab, params, response) => {
let locator: playwright.Locator | undefined;
if (params.selectors && params.selectors.length > 0) {
const resolutionResults = await tab.resolveElementLocators(
params.selectors
);
const successfulResults = resolutionResults.filter(
(r) => r.locator && !r.error
);
if (successfulResults.length === 0) {
const errors = resolutionResults
.map((r) => r.error || 'Unknown error')
.join(', ');
throw new Error(`Failed to resolve element selectors: ${errors}`);
}
locator = successfulResults[0].locator;
response.addCode(
`await page.${await generateLocator(locator)}.evaluate(${quote(params.function)});`
);
} else {
response.addCode(`await page.evaluate(${quote(params.function)});`);
}
await tab.waitForCompletion(async () => {
try {
// Use Playwright's internal _evaluateFunction which safely handles string functions
// This method is used by the upstream microsoft/playwright-mcp implementation
interface ReceiverWithEvaluate {
_evaluateFunction(functionString: string): Promise<unknown>;
}
const receiver = (locator ??
tab.page) as unknown as ReceiverWithEvaluate;
const result = await receiver._evaluateFunction(params.function);
const stringifiedResult = JSON.stringify(result, null, 2);
response.addResult(stringifiedResult ?? 'undefined');
} catch (error) {
response.addError(
`JavaScript evaluation failed: ${error instanceof Error ? error.message : String(error)}`
);
}
});
},
});
export default [evaluate];
