JavaScript global variables and local variables

Local variables:

Variables declared within a function, function arguments are local variables

Function nesting:

Each function has its own scope, and local scope nesting occurs

　

 1  var  test = "Publice"; //  global variable  2  function       Fun1 () { 3   var  test = "private1"; //  4  function   Fun2 () { 5  var  test = "privat  E2 "; //  6  };     7 }; 

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Priority level:

In the function body, local variables are higher than global variables, in other words, local variables in the function body override global variables

Declaration in advance:

JavaScript does not have a block-level scope: The function scope of JavaScript is that all variables declared within a function are always visible within the function, in other words, the var i = 1;,i declared in the If block is a local variable of function and can be accessed within functions.

All variables declared within a function are advanced to the top of the function body, example:

1 var i =20; 2 funtion Test () {3     console.log (i);  // output undefined 4  var i =1; 5 if (1==1) {6 i++;} 7 // output 2; 8 }; 　 　　  

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Equivalent to:

1 var i =20; 2 funtion Test () {3     console.log (i);  // output undefined 4  if (1==1) {5  var i = 1; 6 i++;} 7  Console.log (i);  // output 2; 8 }; 　 　　 　

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JavaScript global variables and local variables