JavaScript objects can be thought of as simple collections of name-value pairs. As such, they are similar to:
- Dictionaries in Python.
- Hashes in Perl and Ruby.
- Hash tables in C and C++.
- HashMaps in Java.
- Associative arrays in PHP.
There are two basic ways to create an empty object:
const obj = new Object();
const obj = {};Object.keys，values，entries
对于普通对象，下列这些方法是可用的：
-
Object.keys(obj) —— 返回一个包含该对象所有的键的数组。
-
Object.values(obj) —— 返回一个包含该对象所有的值的数组。
-
Object.entries(obj) —— 返回一个包含该对象所有 [key, value] 键值对的数组。
-
Map.keys()返回可迭代项 -
Object.keys(obj)返回“真正的”数组
Objects Vs Map
- The keys of an
ObjectareStringsorSymbols, where they can be of any value for aMap. - You can get the
sizeof aMapeasily, while you have to manually keep track of size for anObject. - The iteration of maps is in insertion order of the elements.
- An
Objecthas a prototype, so there are default keys in the map. (This can be bypassed usingmap = Object.create(null).)
- Use maps over objects when keys are unknown until run time, and when all keys are the same type and all values are the same type.
- Use maps if there is a need to store primitive values as keys because object treats each key as a string whether it’s a number value, boolean value or any other primitive value.
- Use objects when there is logic that operates on individual elements.
Objects Prototype
Object prototypes - Learn web development | MDN
Every object in JavaScript has a built-in property, which is called its prototype. The prototype is itself an object, so the prototype will have its own prototype, making what’s called a prototype chain. The chain ends when we reach a prototype that has null for its own prototype.