In your case you may use concat method of Array which can accept single objects as well as array (and even combined):

function myFunc(stringOrArray)
{
  var arr = [].concat(stringOrArray);

  console.log(arr);

  arr.forEach(function(item, i)
  {
    console.log(i, "=", item);
  })
}

myFunc("one string");

myFunc(["one string", "second", "third"]);

concat seems to be one of the oldest methods of Array (even IE 5.5 knows it well).

If the only two kinds of values that could be passed to this function are a string or an array of strings, keep it simple and use a typeof check for the string possibility:

function someFunc(arg) {
    var arr = (typeof arg == "string") ? [arg] : arg;
}

A = [1,2,3]
console.log(A.map==[].map)

In search for shortest version here is what I got so far.

Note, there is no perfect function that will always detect all possible combinations. It is better to know all abilities and limitations of your tools than expect a magic tool.

You could is isArray method but I would prefer to check with

Object.getPrototypeOf(yourvariable) === Array.prototype

I know, that people are looking for some kind of raw javascript approach. But if you want think less about, take a look here: http://underscorejs.org/#isArray

_.isArray(object) 

Returns true if object is an Array.

(function(){ return _.isArray(arguments); })();
=> false
_.isArray([1,2,3]);
=> true

https://developer.mozilla.org/zh-CN/docs/JavaScript/Reference/Global_Objects/Array/isArray

Array.isArray = Array.isArray || function (vArg) {
    return Object.prototype.toString.call(vArg) === "[object Array]";
};

您可以检查变量的类型是否为数组；

var myArray=[];

if(myArray instanceof Array)
{
....
}

考虑到以下评论，这是我尝试改进此答案的尝试：

var isArray = myArray && myArray.constructor === Array;

它摆脱了if / else，并考虑了数组为null或undefined的可能性

我将提供一个功能来测试您要处理的对象的类型...

function whatAmI(me){ return Object.prototype.toString.call(me).split(/\W/)[2]; }

// tests
console.log(
  whatAmI(["aiming","@"]),
  whatAmI({living:4,breathing:4}),
  whatAmI(function(ing){ return ing+" to the global window" }),
  whatAmI("going to do with you?")
);

// output: Array Object Function String

那么您可以编写一个简单的if语句...

if(whatAmI(myVar) === "Array"){
    // do array stuff
} else { // could also check `if(whatAmI(myVar) === "String")` here to be sure
    // do string stuff
}

我用一种非常简单的方式来做。为我工作。有什么缺点吗？

Array.prototype.isArray = true;

a=[]; b={};
a.isArray  // true
b.isArray  // (undefined -> false)

这个问题只有一种解决方案

x instanceof Array

其中x是变量，如果x是数组，它将返回true，否则返回false。

简单的功能检查一下：

function isArray(object)
{
    return object.constructor === Array;
}

这是所有方法中最快的方法（支持所有浏览器）：

function isArray(obj){
    return !!obj && obj.constructor === Array;
}

jQuery还提供了一种$.isArray()方法：

var a = ["A", "AA", "AAA"];

if($.isArray(a)) {
  alert("a is an array!");
} else {
  alert("a is not an array!");
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>

我将首先检查您的实现是否支持isArray：

if (Array.isArray)
    return Array.isArray(v);

您也可以尝试使用instanceof运算符

v instanceof Array