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Standard library

There is a newer version: 3.39.0

'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);
  }
});