ses/src/cauterize-property.js

Hardened JavaScript for Fearless Cooperation

import { objectHasOwnProperty } from './commons.js';

/**
 * @import {Reporter} from './reporting-types.js'
 */

/**
 * Delete `obj[prop]` or at least make it harmless.
 *
 * If the property was not expected, then emit a reporter-dependent warning
 * to bring attention to this case, so someone can determine what to do with it.
 *
 * If the property to be deleted is a function's `.prototype` property, this
 * will normally be because the function was supposed to be a
 * - builtin method or non-constructor function
 * - arrow function
 * - concise method
 *
 * all of whom are not supposed to have a `.prototype` property. Nevertheless,
 * on some platforms (like older versions of Hermes), or as a result of
 * some shim-based mods to the primordials (like core-js?), some of these
 * functions may accidentally be more like `function` functions with
 * an undeletable `.prototype` property. In these cases, if we can
 * set the value of that bogus `.prototype` property to `undefined`,
 * we do so, issuing a warning, rather than failing to initialize ses.
 *
 * @param {object} obj
 * @param {PropertyKey} prop
 * @param {boolean} known If deletion is expected, don't warn
 * @param {string} subPath Used for warning messages
 * @param {Reporter} reporter Where to issue warning or error.
 * @returns {void}
 */
export const cauterizeProperty = (
  obj,
  prop,
  known,
  subPath,
  { warn, error },
) => {
  // Either the object lacks a permit or the object doesn't match the
  // permit.
  // If the permit is specifically false, not merely undefined,
  // this is a property we expect to see because we know it exists in
  // some environments and we have expressly decided to exclude it.
  // Any other disallowed property is one we have not audited and we log
  // that we are removing it so we know to look into it, as happens when
  // the language evolves new features to existing intrinsics.
  if (!known) {
    warn(`Removing ${subPath}`);
  }
  try {
    delete obj[prop];
  } catch (err) {
    if (objectHasOwnProperty(obj, prop)) {
      if (typeof obj === 'function' && prop === 'prototype') {
        obj.prototype = undefined;
        if (obj.prototype === undefined) {
          warn(`Tolerating undeletable ${subPath} === undefined`);
          return;
        }
      }
      error(`failed to delete ${subPath}`, err);
    } else {
      error(`deleting ${subPath} threw`, err);
    }
    throw err;
  }
};