es.string.starts-with.js 1.5 KB

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  1. 'use strict';
  2. var $ = require('../internals/export');
  3. var uncurryThis = require('../internals/function-uncurry-this-clause');
  4. var getOwnPropertyDescriptor = require('../internals/object-get-own-property-descriptor').f;
  5. var toLength = require('../internals/to-length');
  6. var toString = require('../internals/to-string');
  7. var notARegExp = require('../internals/not-a-regexp');
  8. var requireObjectCoercible = require('../internals/require-object-coercible');
  9. var correctIsRegExpLogic = require('../internals/correct-is-regexp-logic');
  10. var IS_PURE = require('../internals/is-pure');
  11. var stringSlice = uncurryThis(''.slice);
  12. var min = Math.min;
  13. var CORRECT_IS_REGEXP_LOGIC = correctIsRegExpLogic('startsWith');
  14. // https://github.com/zloirock/core-js/pull/702
  15. var MDN_POLYFILL_BUG = !IS_PURE && !CORRECT_IS_REGEXP_LOGIC && !!function () {
  16. var descriptor = getOwnPropertyDescriptor(String.prototype, 'startsWith');
  17. return descriptor && !descriptor.writable;
  18. }();
  19. // `String.prototype.startsWith` method
  20. // https://tc39.es/ecma262/#sec-string.prototype.startswith
  21. $({ target: 'String', proto: true, forced: !MDN_POLYFILL_BUG && !CORRECT_IS_REGEXP_LOGIC }, {
  22. startsWith: function startsWith(searchString /* , position = 0 */) {
  23. var that = toString(requireObjectCoercible(this));
  24. notARegExp(searchString);
  25. var index = toLength(min(arguments.length > 1 ? arguments[1] : undefined, that.length));
  26. var search = toString(searchString);
  27. return stringSlice(that, index, index + search.length) === search;
  28. }
  29. });