var isFunction = function isFunction( obj ) {
// Support: Chrome <=57, Firefox <=52
// In some browsers, typeof returns "function" for HTML <object> elements
// (i.e., `typeof document.createElement( "object" ) === "function"`).
// We don't want to classify *any* DOM node as a function.
return typeof obj === "function" && typeof obj.nodeType !== "number";
};

var class2type = {};
var toString = class2type.toString;
// Populate the class2type map，這里并沒有undefined
jQuery.each( "Boolean Number String Function Array Date RegExp Object Error Symbol".split( " " ),
function( i, name ) {
class2type[ "[object " + name + "]" ] = name.toLowerCase();
} );
function toType( obj ) {
if ( obj == null ) {
return obj + "";
}
// Support: Android <=2.3 only (functionish RegExp)
return typeof obj === "object" || typeof obj === "function" ?
class2type[ toString.call( obj ) ] || "object" :
typeof obj;
}

1 if(typeof obj === "object" || typeof obj === "function"){
2 // 因為上文提到存在typeof /s/ 為 function的情況，所以需要toString詳細判斷
3 // 對于判斷不出的數(shù)據(jù)類型默認為object
4 retrun class2type[ toString.call( obj ) ] || "object";
5 } else {
6 // 通過上面typeof對類型判斷的表格，判斷非object function還是很可靠的，所以直接用原生方法
7 return typeof obj;
8 }

var isWindow = function isWindow( obj ) {
return obj != null && obj === obj.window;
};

function isArrayLike( obj ) {
// Support: real iOS 8.2 only (not reproducible in simulator)
// `in` check used to prevent JIT error (gh-2145)
// hasOwn isn't used here due to false negatives
// regarding Nodelist length in IE
var length = !!obj && "length" in obj && obj.length,
type = toType( obj );
if ( isFunction( obj ) || isWindow( obj ) ) {
return false;
}
return type === "array" || length === 0 ||
typeof length === "number" && length > 0 && ( length - 1 ) in obj;
}