ES6 the symbol of entry

The ES5 object property name is a string that can easily cause a violation of property names.

Eg:var a = {name: ' lucy '};a.name = ' Lili ';
This will override the property

ES6 introduces a new primitive data type, symbol, that represents a unique value.

Re-review the new knowledge: There are 6 basic data types: Undefined, Null, Boolean (Boolean), String (string), numeric (number), objects (object).

Here's a new addition: Symbol

Note that the Symbol command cannot be used before the function new , otherwise it will be an error. This is because the generated symbol is a value of the original type, not an object

SymbolA function can accept a string as a parameter, representing a description of the symbol instance, primarily for display in the console, or for a string, to be easily distinguishable.

// Conditions without parameters var s1 = Symbol (); var s2 =//  false//  parameter in case var s1 = Symbol ("foo") ; var s2 = Symbol ("foo"//  false

Symbol values cannot be evaluated with other types of values

Symbol as the property name

varMysymbol =Symbol ();//The first form of a notationvarA ={};a[mysymbol]= ' hello! ';//The second type of notationvarA ={[Mysymbol]:' Hello! '};//The Third kind of wordingvarA ={};object.defineproperty (A, Mysymbol, {value:' Hello! ' });//The same result is found in the above notationA[mysymbol]//"Hello!"

Note that you cannot use the dot operator when the symbol value is used as the object property name.

var a = {}; var name == ' Lili '= ' Lucy '; Console.log (A.name,a[name]);              // Lili,lucy

When a symbol value is a property name, the property is also exposed, not a private property.

This is somewhat similar to the protected attribute in Java (the difference between protected and private: The outside of the class is inaccessible, subclasses within a class can inherit protected can not inherit private)

But the symbol here is also accessible outside the class, but it will not appear in for...in , for...of loop, or be Object.keys() Object.getOwnPropertyNames() returned. But there is a Object.getOwnPropertySymbols way to get all the symbol property names for the specified object

Symbol.for (), Symbol.keyfor ()

The symbol.for mechanism is somewhat analogous to a singleton pattern, first searching globally for a symbol value with that parameter as its name, and if so, returns the symbol value, or creates a new and returns a symbol value that is the name of the string. and the direct symbol is a little different.

var s1 = Symbol.  for (' foo '); var s2 = Symbol.  for (' foo '//  true

The Symbol.keyfor method returns a key for a registered symbol type value. The essence is to detect whether the symbol has been created

var s1 = Symbol.  for ("foo"//  "foo"var s2 = Symbol ("foo"//  undefined

Built-in symbol value

There are 11 ways to view http://es6.ruanyifeng.com/#docs/symbol

ES6 the symbol of entry