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Object - Coggle Diagram

- - - - freezing objects and arrays.
      - make an object immutable.
    - - Determine if an object is frozen or not
      - Object.isFrozen(object)
  - - - both undefined
      - both null
      - both true or both false
      - both strings of the same length with the same characters in the same order
      - both the same object (means both object have same reference)
      - both numbers and both +0 both -0 both NaN both non-zero and both not NaN and both have the same value.
  - - - sealing objects and arrays.
      - make an object immutable.
    - - determine if an object is sealed or not
      - Object.isSealed(object)
- - - - Object.assign.
        
        It copies the properties of all source objects into the target dest
        
        Object.assign(dest, ...sources)
        
        Nested cloning
        
        With property is object, property's of object clone will reference to this object
      - basic duplicate
        
        using for in loop
      - structuredClone
        
        clones the object with all nested properties
        
        can clone most data types, such as objects, arrays, primitive values.
        
        supports circular references
  - - - "this" is the "current object"
    - - Calling without an object: this == undefined
      - The value of this is defined at run-time
      - this has no value until the function is called.
- - - - Objects are retained in memory while they are reachable.
  - - - Create object
    - - check whether it was called with new or without it
    - - Return object it will be object
      - Other all cases will return this
  - - - create “hidden” properties of an object
        
        other part of code can accidentally access or overwrite.
    - - Symbol.for
      - Symbol.for(key)
  - - - string
      - number
      - default
    - - it must return a primitive, otherwise there will be an error.
    - - For the "string" hint
        
        call toString method
        
        if it doesn’t exist or if it returns an object instead of a primitive value, then call valueOf
      - For other hints
        
        call valueOf
        
        if it doesn’t exist or if it returns an object instead of a primitive value, then call toString
      - plain object
        
        toString
        
        returns a string "[object Object]"
        
        valueOf
        
        returns the object itself.
  - - - Object.defineProperties(obj, descriptors) that allows to define many properties at once.
      - To change the flags, we can use Object.defineProperty.
      - Object.getOwnPropertyDescriptor allows to query the full information about a property
    - - configurable
      - writable
      - enumerable
    - - let clone = Object.defineProperties({}, Object.getOwnPropertyDescriptors(obj));
        
        object have been clonse have all property descriptors including symbolic and non-enumerable ones.
    - - methods that limit access to the whole object
        
        Object.seal(obj)
        
        Forbids adding/removing of properties. Sets configurable: false for all existing properties.
        
        Object.preventExtensions(obj)
        
        Forbids the addition of new properties to the object.
        
        Object.freeze(obj)
        
        Forbids adding/removing/changing of properties. Sets configurable: false, writable: false for all existing properties.
      - Property descriptors work at the level of individual properties.
      - here are tests for those method
        
        Object.isExtensible(obj)
        
        Returns false if adding properties is forbidden, otherwise true.
        
        Object.isSealed(obj)
        
        Returns true if adding/removing properties is forbidden, and all existing properties have configurable: false.
        
        Object.isFrozen(obj)
        
        Returns true if adding/removing/changing properties is forbidden, and all current properties are configurable: false, writable: false.
  - - - with defineProperty, we can pass a descriptor with get and set
      - note that a property can be either an accessor (has get/set methods) or a data property (has a value), not both.
        
        It mean not the same when using defineProperty method
- - - - Object.entries(obj).length === 0 && obj.constructor === Object;
    - - Object.keys(obj).length === 0 && obj.constructor === Object
  - - - if two object have same property then target.property has been overite
      - Object.assign(target, ...sources);
      - benefit
        
        cloning an object.
        
        merge objects with the same properties.
  - - - objectName.property;
    - - objectName["property"];
    - - objectName[expression];
  - - - object.key3 = "value3";
    - - obj["key3"] = "value3";
  - - - "key" in obj;
      - !("key" in obj);
    - - obj.hasOwnProperty("key"); // true
    - - user.name !== undefined
      - access a non-existing property from an object, the result is undefined