core-js/internals/is-constructor.js

'use strict';
var uncurryThis = require('../internals/function-uncurry-this');
var fails = require('../internals/fails');
var isCallable = require('../internals/is-callable');
var classof = require('../internals/classof');
var getBuiltIn = require('../internals/get-built-in');
var inspectSource = require('../internals/inspect-source');

var noop = function () { /* empty */ };
var construct = getBuiltIn('Reflect', 'construct');
var constructorRegExp = /^\s*(?:class|function)\b/;
var exec = uncurryThis(constructorRegExp.exec);
var INCORRECT_TO_STRING = !constructorRegExp.test(noop);

var isConstructorModern = function isConstructor(argument) {
  if (!isCallable(argument)) return false;
  try {
    construct(noop, [], argument);
    return true;
  } catch (error) {
    return false;
  }
};

var isConstructorLegacy = function isConstructor(argument) {
  if (!isCallable(argument)) return false;
  switch (classof(argument)) {
    case 'AsyncFunction':
    case 'GeneratorFunction':
    case 'AsyncGeneratorFunction': return false;
  }
  try {
    // we can't check .prototype since constructors produced by .bind haven't it
    // `Function#toString` throws on some built-it function in some legacy engines
    // (for example, `DOMQuad` and similar in FF41-)
    return INCORRECT_TO_STRING || !!exec(constructorRegExp, inspectSource(argument));
  } catch (error) {
    return true;
  }
};

isConstructorLegacy.sham = true;

// `IsConstructor` abstract operation
// https://tc39.es/ecma262/#sec-isconstructor
module.exports = !construct || fails(function () {
  var called;
  return isConstructorModern(isConstructorModern.call)
    || !isConstructorModern(Object)
    || !isConstructorModern(function () { called = true; })
    || called;
}) ? isConstructorLegacy : isConstructorModern;