src/privates/_isArrayIndex.js
function _isArrayIndex (target, key) {
    var n = +key;

    return Array.isArray(target) && n % 1 === 0 && !(n < 0 && _isEnumerable(target, key));
}
function _isArrayIndex (target, key) {
    var n = +key;

    return Array.isArray(target) && n % 1 === 0 && !(n < 0 && _isEnumerable(target, key));
}
function _isArrayIndex ( target , key ) { var n = + key ; return Array . isArray ( target ) && n % 1 === 0 && ! ( n < 0 && _isEnumerable ( target , key ) ) ; }
Accepts a target object and a key name and verifies that the target is an array and that
the key is an existing index.
@private
@param {Object} target
@param {String|Number} key
@returns {Boolean}
Accepts a target object and a key name and verifies that the target is an array and that the key is an existing index .