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1<! DOCTYPE html>234<meta charset= "Utf-8" >5<title></title>67<body>8<script type= "Text/javascript" >9 /*Ten a variable scope (scope) is defined in the program source code . One the area. A Global variables have global scope, but variables declared within a function - defined in the function body only, they are local variables, the scope is local - function arguments are also local variables, which are defined only within the function body*/ the - //local variables have precedence over global variables with the same name - //----> If a local variable or function argument is declared within a function with the same name as a variable and a global variable - //----> Global variables are obscured by local variables + varScope= "Global";//declaring a global variable - functionCheckscope () { + A varScope= "Local";//declaring the same local variable at returnScope//returns the value of a local variable, not the value of a global variable - - - } - Checkscope () - inConsole.log (Checkscope ())//"Local" - to //--->1--global scope You can write code without writing the VAR statement, you must use the VAR statement when declaring a local variable +Scope= "Global";//declare a global variable, even without Var - functioncheckscope2 () { theScope= "Local";//the global variable was modified *Myscope= "Local"//here, a new global variable is declared. $ return[Scope,myscope];//returns a value of twoPanax Notoginseng } -Checkscope2 ()//function Call theConsole.log (Checkscope2 ())//=>["local", "local"] + //---->2--function definition can be nested, because each function has its own scope, so there will be a number of local action nesting cases A the varScope= "Global scope";//Global Variables + functionCheckscope () { - varScope= "local scope";//Local Variables $ functionnested () { $ varScope = "nested scope";//local variables within a nested scope - returnScope//returns the value in the current scope - the } -Nested ()//nested function callsWuyi the } -Checkscope ()//= = "Nested scopes" Wu - /* About function scope and declaration in advance $ 1---> C-like programming-each piece of code within the curly braces has its own scope - and variables are not visible outside of the code snippet that declares them, called Block-level scopes (block scope) - There is no block-level scope in JavaScript - JavaScript instead uses the function scope: A Variables are defined in the body of the function in which they are declared and in the body of any function nested within the function body. + the */ - //----1--> $ functionTest (o) { the vari=0;//I have a definition in the whole function body the if(typeofo== "Object"){ the varj=0;//j is defined in the function body, not just within this code snippet the for(vark=0;k<10;k++) {//k is defined in the function body, not just within the loop -Console.log (k);//Output Digital 0~9 in the the } About theConsole.log (k);//k already defined, output the } theConsole.log (j);//J has been defined, but may not be initialized + } - //The function scope of JavaScript is that all variables declared within a function are always visible inside the function body the //means that the variable is even available before the Declaration, and that the JavaScript feature is informally called a declaration in advanceBayi the //The JavaScript function declares that all variables are advanced to the inside of the function body. the varScope= "Global"; - functionf () { - theConsole.log (scope);//output Undefind, "instead of" global " the varScope= "Local";//The variable assigns the initial value here, but the variable itself is defined anywhere within the function body theConsole.log (scope);//output "local" the } - the the</script> the 94</body> theJavaScript variable Scope
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