A data type in JSl

It can be understood as an unordered data collection. Note that an array is an ordered data collection.

Used to describe something, such as a person

Object declaration syntax

Objects are composed of properties and methods

Attributes

operate

Information about data behavior is called methods, such as running, singing, etc., which are generally verbs, and their essence is a function.

Methods are composed of two parts: method name and function. They are separated by:

Use English to separate multiple attributes

Methods are functions attached to an object

Method names can use "" or '', which are generally omitted unless the name encounters special symbols such as spaces, dashes, etc.

After declaring an object and adding several methods, you can use it to call functions in the object, which is called method calling.

You can also add formal parameters and actual parameters

Note: Parentheses need to be added after the method name.

grammar

Generally, this method is not used to traverse arrays. It is mainly used to traverse objects.

The k in the for in syntax is a variable, which represents the attribute name of the object in turn during the loop.

Since k is a variable, it must be parsed using [] syntax

Be sure to remember: k is the attribute name of the object, and the object name [k] is the attribute value.

The object provided internally by JS contains various properties and methods for developers to call

Built-in object-Math

string, number, boolean, undefined, null

Object,Array,Date