ECMAScript variables:
1. Basic type value (simple data segment)
2. Type reference value (the object may be made of values over) → objects stored in memory
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Dynamic properties: only give type reference value dynamically add new attributes for future use.
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Copy the variable value:
Copy primitive values → create a new variable object on the value of the new variable → copy to (independently of each other)
Copy Copy → reference value stored in the variable object to a type value of a new variable allocation space (copied is a pointer to the same object, interaction)
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The arguments:
ECMAScript functions for all the parameters are passed by value.
(Outside of the function to the parameter in the copy function.
→ ECMA function parameters can imagine local variables. )
Explain the reasons:
A statement:
Parameters are a function of local variables, the parameters passed to the function in the external value of internal and external non-interacting, replication is passed by reference address, so he House external influence each other.
Argument 2: The object angle (parameter is an object obj)
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Object parameters passed by value → → reference external object and objects outside the object of the same object point in the object is only a heap memory, and is a global variable.
Do not be mistaken in the role of a local variable in local modify objects in the global scope (external) reflected in the results of → internal function of executing the function will be immediately destroyed.
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Execution Environment (sometimes also referred to as "Environment") and Scope
Execution environment defines all variables and functions white Niang function or have access to other data determine their own behavior → each execution environment has an associated variable object → defined in the environment are stored in this object.
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Each function has its own execution environment → execution flow when entering a function → function of the ambient environment will be pushed into a stack to perform its function after → → pop-up before returning control to the execution environment of
code in a single environment execution, it creates a variable object scope chain (scope chain)
Scope chain purposes: to ensure orderly access to all variables and functions have access to the execution environment.
The front of the scope chain, is always variable object code environment where the currently executing
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Internal environment through the scope chain all of the external environment, the external environment can not access the internal environment (environmental contact is linear, orderly → up search scope chain to check variable and function names)
Function parameters are also treated as a variable
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Extend the scope chain:
Some statements can be a temporary increase in front-end chain variable scope (variable removed after code execution)
1.try-catch catch block statements
2.with statement
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No block-level scope Javas
ECMAScript variables:
1. Basic type value (simple data segment)
2. Type reference value (the object may be made of values over) → objects stored in memory
------
Dynamic properties: only give type reference value dynamically add new attributes for future use.
------
Copy the variable value:
Copy primitive values → create a new variable object on the value of the new variable → copy to (independently of each other)
Copy Copy → reference value stored in the variable object to a type value of a new variable allocation space (copied is a pointer to the same object, interaction)
------
The arguments:
ECMAScript functions for all the parameters are passed by value.
(Outside of the function to the parameter in the copy function.
→ ECMA function parameters can imagine local variables. )
Explain the reasons:
A statement:
Parameters are a function of local variables, the parameters passed to the function in the external value of internal and external non-interacting, replication is passed by reference address, so he House external influence each other.
Argument 2: The object angle (parameter is an object obj)
------
Object parameters passed by value → → reference external object and objects outside the object of the same object point in the object is only a heap memory, and is a global variable.
Do not be mistaken in the role of a local variable in local modify objects in the global scope (external) reflected in the results of → internal function of executing the function will be immediately destroyed.
------
Execution Environment (sometimes also referred to as "Environment") and Scope
Execution environment defines all variables and functions white Niang function or have access to other data determine their own behavior → each execution environment has an associated variable object → defined in the environment are stored in this object.
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每个函数都有自己的执行环境 → 当执行流进入一个函数时 → 函数环境会被推入一个环境栈中 → 在函数执行后将其弹出 → 把控制权返回给之前的执行环境
代码在一个环境执行中时，会创建变量对象的一个作用域链（scope chain）
作用域链用途：保证对执行环境有权访问的所有变量和函数的有序访问。
作用域链的前端，始终都是当前执行的代码所在环境的变量对象
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内部环境可以通过作用域链所有的外部环境，但是外部环境不能访问内部环境（环境的联系是线性的，有次序的 → 向上搜索作用域链以查询变量和函数名）
函数参数也被当做变量来对待
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延长作用域链：
有些语句可以在作用域的前端链临时增加一个变量（变量在代码执行后移除）
1.try-catch语句的catch块
2.with语句
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Javas没有块级作用域