node/test/parallel/test-repl-context.js

'use strict';
const common = require('../common');
const assert = require('assert');
const repl = require('repl');
const vm = require('vm');

// Create a dummy stream that does nothing
const stream = new common.ArrayStream();

// Test when useGlobal is false
testContext(repl.start({
  input: stream,
  output: stream,
  useGlobal: false
}));

function testContext(repl) {
  const context = repl.createContext();
  // ensure that the repl context gets its own "console" instance
  assert(context.console instanceof require('console').Console);

  // ensure that the repl's global property is the context
  assert.strictEqual(context.global, context);

  // ensure that the repl console instance does not have a setter
  assert.throws(() => context.console = 'foo', TypeError);
  repl.close();
}

testContextSideEffects(repl.start({ input: stream, output: stream }));

function testContextSideEffects(server) {
  assert.ok(!server.underscoreAssigned);
  assert.strictEqual(server.lines.length, 0);

  // an assignment to '_' in the repl server
  server.write('_ = 500;\n');
  assert.ok(server.underscoreAssigned);
  assert.strictEqual(server.lines.length, 1);
  assert.strictEqual(server.lines[0], '_ = 500;');
  assert.strictEqual(server.last, 500);

  // use the server to create a new context
  const context = server.createContext();

  // ensure that creating a new context does not
  // have side effects on the server
  assert.ok(server.underscoreAssigned);
  assert.strictEqual(server.lines.length, 1);
  assert.strictEqual(server.lines[0], '_ = 500;');
  assert.strictEqual(server.last, 500);

  // reset the server context
  server.resetContext();
  assert.ok(!server.underscoreAssigned);
  assert.strictEqual(server.lines.length, 0);

  // ensure that assigning to '_' in the new context
  // does not change the value in our server.
  assert.ok(!server.underscoreAssigned);
  vm.runInContext('_ = 1000;\n', context);

  assert.ok(!server.underscoreAssigned);
  assert.strictEqual(server.lines.length, 0);
  server.close();
}