test/mjsunit/builtins.js

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// Flags: --expose-natives-as=builtins

// Checks that all function properties of the builtin object are neither
// writable nor configurable. Also, theose functions that are actually
// constructors (recognized by having properties on their .prototype object),
// have only unconfigurable properties on the prototype, and the methods
// are also non-writable.

var names = Object.getOwnPropertyNames(builtins);

function isFunction(obj) {
  return typeof obj == "function";
}

function checkConstructor(func, name) {
  // A constructor is a function with a prototype and properties on the
  // prototype object besides "constructor";
  if (name.charAt(0) == "$") return;
  if (typeof func.prototype != "object") return;
  var propNames = Object.getOwnPropertyNames(func.prototype);
  if (propNames.length == 0 ||
      (propNames.length == 1 && propNames[0] == "constructor")) {
    // Not a constructor.
    return;
  }
  var proto_desc = Object.getOwnPropertyDescriptor(func, "prototype");
  assertTrue(proto_desc.hasOwnProperty("value"), name);
  assertFalse(proto_desc.writable, name);
  assertFalse(proto_desc.configurable, name);
  var prototype = proto_desc.value;
  assertEquals(null, prototype.__proto__, name);
  for (var i = 0; i < propNames.length; i++) {
    var propName = propNames[i];
    if (propName == "constructor") continue;
    var testName = name + "-" + propName;
    var propDesc = Object.getOwnPropertyDescriptor(prototype, propName);
    assertTrue(propDesc.hasOwnProperty("value"), testName);
    assertFalse(propDesc.configurable, testName);
    if (isFunction(propDesc.value)) {
      assertFalse(propDesc.writable, testName);
    }
  }
}

for (var i = 0; i < names.length; i++) {
  var name = names[i];
  var desc = Object.getOwnPropertyDescriptor(builtins, name);
  assertTrue(desc.hasOwnProperty("value"));
  var value = desc.value;
  if (isFunction(value)) {
    assertFalse(desc.writable, name);
    assertFalse(desc.configurable, name);
    checkConstructor(value, name);
  }
}