javascript - Difference between Boolean object and basic type Boolean

Question

var a=new Boolean(false);
var b=false;
alert(a instanceof Boolean);
alert(b instanceof Boolean);
The first true pops up
The second one pops up false
Why? I don’t quite understand.

Answer 1

There are two types of values ​​in JavaScript: primitive types and reference types (objects).

false is a boolean primitive value, not an object, so false instanceof Boolean is false.

Similarly, "foo" instanceof String is also false.

Checking primitive types can be done with typeof.

You will see that the value of typeof false is "boolean", note the lowercase "b".

and:

typeof Boolean is "function"
Boolean instanceof Object is true

Since JavaScript performs type conversion silently, users often ignore the differences between types. For example, var length = "hello world".length converts the original type string into an instance of the String object.

Answer 2

var a = new Boolean(false);
var b = false;
alert(typeof a); // 'Object'
alert(typeof b); // 'Boolean'
alert(a === b); // false

Answer 3

instanceof is used to determine whether an object is an instance of a certain constructor.
b is obviously not an object

Answer 4

Except for object, all other types are basic types. What you are here is to determine whether it is a Boolean instance, which belongs to object. The subsequent basic type is false. If it is not a Boolean instance produced by new, the result will of course be false.