Analysis summary of local objects & built-in objects & host objects in js

The content of this article is about the analysis of local objects & built-in objects & host objects in js. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

1. Local objects
ECMA-262 defines a native object as an object that is independent of the ECMAScript implementation of the host environment.
Here is a brief talk about the application environment of JavaScript. The application environment of JavaScript consists of the host environment and the runtime environment. The host environment mainly refers to the shell and web browser, etc. The runtime environment is built in by the JavaScript engine.

Now let’s take a look at what local objects are:
Object, Function, Array, String, Number, Date, RegExp, Boolean, Error, EvalError, RangeError, ReferenceError, SyntaxError, TypeError, URIError

2. Built-in objects
ECMA-262 defines built-in objects as: all objects implemented by ECMAScript that are independent of the host environment and appear when the ECMAScript program starts executing.
This means that the built-in objects have already been instantiated, and we do not need to instantiate them anymore. The first thing we will think of here is the Math object.
There are only two built-in objects defined by ECMA-262: Global and Math. (Local objects and built-in objects are independent of the host object. According to the definition, it can be seen that built-in objects are also local objects. All built-in objects in JS are local objects).

Math object is something we often use, but Global is relatively rare. In fact, we often use the Global object, but we don't use the name Global.

Global object is a special object. It is a global object. There is only one in the program. Its existence is accompanied by the life cycle of the entire program. The global object cannot be accessed by name, but it has a window attribute, this attribute points to itself.
Everyone should also be aware that there are no independent functions in ECMAScript. All functions should be methods of an object. Methods similar to isNaN(), parseInt(), parseFloat(), etc. are all methods of the Global object.

3. Host object
Host object: an object provided by the host environment implemented by ECMAScript.
Maybe this is not easy to understand. As mentioned above, the host environment includes the web browser, so we can understand that the objects provided by the browser are host objects.
It can also be understood this way, because local objects are objects in the non-host environment, then non-local objects are host objects, that is, all BOM objects and DOM objects are host objects.
Then there is another kind of object, which is the object defined by ourselves, which is also the host object.

The simplest understanding: Objects not officially defined by ECMAScript belong to host objects.

4. Summary
Local objects are objects defined in ECMAScript, such as String, Date, etc. Built-in objects are a special type of local objects and do not need to be instantiated. , including Global and Math, the host objects are BOM, DOM and self-defined objects.

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