--- /dev/null
+'use strict';
+var $ = require('../internals/export');
+var uncurryThis = require('../internals/function-uncurry-this');
+var requireObjectCoercible = require('../internals/require-object-coercible');
+var toIntegerOrInfinity = require('../internals/to-integer-or-infinity');
+var toString = require('../internals/to-string');
+
+var stringSlice = uncurryThis(''.slice);
+var max = Math.max;
+var min = Math.min;
+
+// eslint-disable-next-line unicorn/prefer-string-slice -- required for testing
+var FORCED = !''.substr || 'ab'.substr(-1) !== 'b';
+
+// `String.prototype.substr` method
+// https://tc39.es/ecma262/#sec-string.prototype.substr
+$({ target: 'String', proto: true, forced: FORCED }, {
+ substr: function substr(start, length) {
+ var that = toString(requireObjectCoercible(this));
+ var size = that.length;
+ var intStart = toIntegerOrInfinity(start);
+ var intLength, intEnd;
+ if (intStart === Infinity) intStart = 0;
+ if (intStart < 0) intStart = max(size + intStart, 0);
+ intLength = length === undefined ? size : toIntegerOrInfinity(length);
+ if (intLength <= 0 || intLength === Infinity) return '';
+ intEnd = min(intStart + intLength, size);
+ return intStart >= intEnd ? '' : stringSlice(that, intStart, intEnd);
+ }
+});