core-js/internals/to-index.js

Standard library

var toInteger = require('../internals/to-integer');
var toLength = require('../internals/to-length');

// `ToIndex` abstract operation
// https://tc39.es/ecma262/#sec-toindex
module.exports = function (it) {
  if (it === undefined) return 0;
  var number = toInteger(it);
  var length = toLength(number);
  if (number !== length) throw RangeError('Wrong length or index');
  return length;
};