How to use 'typeof undefined' in JavaScript

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39function typeOf(object) {
40 if (typeof object === 'object' && object !== null) {
41 var $$typeof = object.$$typeof;
42
43 switch ($$typeof) {
44 case REACT_ELEMENT_TYPE:
45 var type = object.type;
46
47 switch (type) {
48 case REACT_ASYNC_MODE_TYPE:
49 case REACT_FRAGMENT_TYPE:
50 case REACT_PROFILER_TYPE:
51 case REACT_STRICT_MODE_TYPE:
52 return type;
53 default:
54 var $$typeofType = type && type.$$typeof;
55
56 switch ($$typeofType) {
57 case REACT_CONTEXT_TYPE:
58 case REACT_FORWARD_REF_TYPE:
59 case REACT_PROVIDER_TYPE:
60 return $$typeofType;
61 default:
62 return $$typeof;
63 }
64 }
65 case REACT_PORTAL_TYPE:
66 return $$typeof;
67 }
68 }
69
70 return undefined;
71}
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14function typeOf(object) {
15 var type = typeof object;
16 if (type === 'undefined') {
17 return 'undefined';
18 }
19 if (object) {
20 type = object.constructor.name;
21 } else if (type === 'object') {
22 type = toString.call(object).slice(8, -1);
23 }
24 return type.toLowerCase();
25}

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