JavaScript runtime environment and scope chain

operating Environment : the environment in which JavaScript code snippets are executed (can be understood as scopes in C/s + +)"Personal understanding"

Variable Object : The first is an object that holds all the variables and functions of the current execution environment (JavaScript functions can be nested, C + + is not as if (the new version seems to be possible))

Correspondence Relationship : Each execution environment has an associated variable object

scope chain : chain, linked list.

Function: Ensures an orderly access to all variables and functions that the execution environment has access to (what ghost, the language of the test?) ）

Current variable object → variable object containing environment → variable object containing environment ... → Global execution object's variable object

Note: There is no concept of block-level scope in JavaScript

if (true) {    var color = ' red ';} Console.log (color);

is correct in JavaScript and is incorrect in C + +

The following code is problematic

function Outfun () {    var color1 = ' yellow ';     function Innerfun ()  {        var color2 = ' green ';    }    Console.log (COLOR2); // not correct }

Why is it wrong? JS is not a block-level scope, yes there is no block-level scope. But there is an execution environment (scope)

The execution environment of the COLOR2 here is valid in Innerfun (the scope of C + + is understood)

JavaScript runtime environment and scope chain