Why JS typeof null is object

why typeof nullthe result isObject

null是基本类型 而object 是引用类型 这样就会存在矛盾

 Let's analyze this problem from the source code. Our JS is compiled by the V8 engine, so we need to debug V8

The installation tool node version should be higher

npm install -g jsvu

Install the V8 engine

jsvu --os=win64 --engines=v8-debug
//os 根据自己的操作系统选择

 Switch to .jsvu under the user directory

 Generate bytecode by the following command

v8-debug -e --print-bytecode --allow-natives-syntax "var x = xxxx"

 Conclusions from generated bytecode

type of data	Machine code identifies the object
(Object)	000
integer	1
floating point number	010
string	100
Boolean	110
null	all 0

Look at the source code of typeOf

 JS_PUBLIC_API(JSType)
    JS_TypeOfValue(JSContext *cx, jsval v)
    {
        JSType type = JSTYPE_VOID;
        JSObject *obj;
        JSObjectOps *ops;
        JSClass *clasp;

        CHECK_REQUEST(cx);
        if (JSVAL_IS_VOID(v)) {  // (1)
            type = JSTYPE_VOID;
        } else if (JSVAL_IS_OBJECT(v)) {  // (2)
            obj = JSVAL_TO_OBJECT(v);
            if (obj &&
                (ops = obj->map->ops,
                 ops == &js_ObjectOps
                 ? (clasp = OBJ_GET_CLASS(cx, obj),
                    clasp->call || clasp == &js_FunctionClass) // (3,4)
                 : ops->call != 0)) {  // (3)
                type = JSTYPE_FUNCTION;
            } else {
                type = JSTYPE_OBJECT;
            }
        } else if (JSVAL_IS_NUMBER(v)) {
            type = JSTYPE_NUMBER;
        } else if (JSVAL_IS_STRING(v)) {
            type = JSTYPE_STRING;
        } else if (JSVAL_IS_BOOLEAN(v)) {
            type = JSTYPE_BOOLEAN;
        }
        return type;
    }

When judging the data type, it is judged according to the low-order flag of the machine code, and nullthe machine code flag of is full 0, and the low-order flag of the object's machine code is 000. So typeof nullthe result is misjudged asObject