JS operators and expressions \ flow structure of functions and programs

  Operator ： A group of symbols that can complete data calculation

• Arithmetic operator +（ Representing addition , It can also be used for string connection ） -( The minus sign can also be a minus sign ) * / % 
• ++ Self increasing -- Self reduction
• ++ There are differences before and after variables
• Relational operator -- Judge the direct size relationship of data ><= etc.

 == be equal to , Do not compare type values compare values

=== Congruence ： In addition to the values , Types will also be compared

The result of the relational operator is True  False

• Logical operators -- The associated condition   && And || or ！ Not
• A short circuit && A short circuit ||
• Conditional operator === Ternary operator 1？2：3

expression ： The composition of operators and operands is formula , Each expression has a value

function ：function：  It's all right Can be used repeatedly （ Code block ） It is allowed to contain multiple executable codes

usage ：

        function Function name （）{

        Executable statement ;

}

Function call ;

         The name of the function （）

---

Define a function with parameters ：

usage ：

        function Function name （ Parameters （ Shape parameter ） list （ Consists of one or more variable names ） Statement ）{

        Executable statement ;

}

call Functions with parameters ： ​​​​​​​ The name of the function （ Actual parameters ）

---

Define a function with a return value ：

usage ：

        function Function name （ Parameters （ Shape parameter ） list （ Consists of one or more variable names ） Declared or not ）{

        Executable statement ;

        return value ;

}

call Functions with parameters ： ​​​​​​​ The name of the function （ Actual parameters ）

•   Scope ： Accessible range of variables or functions
• Function scope ： Access only within the current function
• Global scope ： After definition , Code can be accessed anywhere

Variable of function scope ： local variable -- Only the current function can access

Global variables , Outside the function , It can only be defined once

Sequential execution 、 Branch out