ses/src/global-object.js

Hardened JavaScript for Fearless Cooperation

import {
  TypeError,
  assign,
  create,
  defineProperty,
  entries,
  freeze,
  hasOwn,
  unscopablesSymbol,
} from './commons.js';
import { makeEvalFunction } from './make-eval-function.js';
import { makeFunctionConstructor } from './make-function-constructor.js';
import { constantProperties, universalPropertyNames } from './permits.js';

/**
 * The host's ordinary global object is not provided by a `with` block, so
 * assigning to Symbol.unscopables has no effect.
 * Since this shim uses `with` blocks to create a confined lexical scope for
 * guest programs, we cannot emulate the proper behavior.
 * With this shim, assigning Symbol.unscopables causes the given lexical
 * names to fall through to the terminal scope proxy.
 * But, we can install this setter to prevent a program from proceding on
 * this false assumption.
 *
 * @param {object} globalObject
 */
export const setGlobalObjectSymbolUnscopables = globalObject => {
  defineProperty(
    globalObject,
    unscopablesSymbol,
    freeze(
      assign(create(null), {
        set: freeze(() => {
          throw TypeError(
            `Cannot set Symbol.unscopables of a Compartment's globalThis`,
          );
        }),
        enumerable: false,
        configurable: false,
      }),
    ),
  );
};

/**
 * setGlobalObjectConstantProperties()
 * Initializes a new global object using a process similar to ECMA specifications
 * (SetDefaultGlobalBindings). This process is split between this function and
 * `setGlobalObjectMutableProperties`.
 *
 * @param {object} globalObject
 */
export const setGlobalObjectConstantProperties = globalObject => {
  for (const [name, constant] of entries(constantProperties)) {
    defineProperty(globalObject, name, {
      value: constant,
      writable: false,
      enumerable: false,
      configurable: false,
    });
  }
};

/**
 * setGlobalObjectMutableProperties()
 * Create new global object using a process similar to ECMA specifications
 * (portions of SetRealmGlobalObject and SetDefaultGlobalBindings).
 * `newGlobalPropertyNames` should be either `initialGlobalPropertyNames` or
 * `sharedGlobalPropertyNames`.
 *
 * @param {object} globalObject
 * @param {object} args
 * @param {object} args.intrinsics
 * @param {object} args.newGlobalPropertyNames
 * @param {Function} args.makeCompartmentConstructor
 * @param {(object) => void} args.markVirtualizedNativeFunction
 * @param {Compartment} [args.parentCompartment]
 */
export const setGlobalObjectMutableProperties = (
  globalObject,
  {
    intrinsics,
    newGlobalPropertyNames,
    makeCompartmentConstructor,
    markVirtualizedNativeFunction,
    parentCompartment,
  },
) => {
  for (const [name, intrinsicName] of entries(universalPropertyNames)) {
    if (hasOwn(intrinsics, intrinsicName)) {
      defineProperty(globalObject, name, {
        value: intrinsics[intrinsicName],
        writable: true,
        enumerable: false,
        configurable: true,
      });
    }
  }

  for (const [name, intrinsicName] of entries(newGlobalPropertyNames)) {
    if (hasOwn(intrinsics, intrinsicName)) {
      defineProperty(globalObject, name, {
        value: intrinsics[intrinsicName],
        writable: true,
        enumerable: false,
        configurable: true,
      });
    }
  }

  const perCompartmentGlobals = {
    globalThis: globalObject,
  };

  perCompartmentGlobals.Compartment = freeze(
    makeCompartmentConstructor(
      makeCompartmentConstructor,
      intrinsics,
      markVirtualizedNativeFunction,
      {
        parentCompartment,
        enforceNew: true,
      },
    ),
  );

  // TODO These should still be tamed according to the permits before
  // being made available.
  for (const [name, value] of entries(perCompartmentGlobals)) {
    defineProperty(globalObject, name, {
      value,
      writable: true,
      enumerable: false,
      configurable: true,
    });
    if (typeof value === 'function') {
      markVirtualizedNativeFunction(value);
    }
  }
};

/**
 * setGlobalObjectEvaluators()
 * Set the eval and the Function evaluator on the global object with given evalTaming policy.
 *
 * @param {object} globalObject
 * @param {Function} evaluator
 * @param {(object) => void} markVirtualizedNativeFunction
 */
export const setGlobalObjectEvaluators = (
  globalObject,
  evaluator,
  markVirtualizedNativeFunction,
) => {
  {
    const f = freeze(makeEvalFunction(evaluator));
    markVirtualizedNativeFunction(f);
    defineProperty(globalObject, 'eval', {
      value: f,
      writable: true,
      enumerable: false,
      configurable: true,
    });
  }
  {
    const f = freeze(makeFunctionConstructor(evaluator));
    markVirtualizedNativeFunction(f);
    defineProperty(globalObject, 'Function', {
      value: f,
      writable: true,
      enumerable: false,
      configurable: true,
    });
  }
};