7.31 sign In, JS Global preprocessing note

JS parsing and execution process:

First, the overall:

1. pretreatment Stage:

1, lexicalenviroment = = = Window {1, pre-processing var |    2, function xxx//Pre-processing declaration functions } Note: A function created without preprocessing a function expression : var g = function ();
2, ECMA-262 variableenvironment

　　　　　　　　　　　　　　　　

　　　　　　　　　　　2, the implementation phase:

    Console.log (a);                                    4, the input is the preprocessing phase of function A{return 6;}    function A () {     return  document.documentElement.OffsetWidth;     1. First preprocess function A ()    }    function A () {     return  6;                                        2. Overwrite function A ()    }     var a = 3;                                        3, VAR declaration variable priority is lower than function, so invalid     a = 3;                                            4, expression A = 3, is the execution phase, covering for a = 3;    Console.log (a);                                    5. The output sequence executes a = 3;

　　

Second, function:

7.31 sign In, JS Global preprocessing note