Eval
Eval (parse) Parse: Inside with the argument string, we know that executing JavaScript compiles and executes,
To change the value of a global variable:
var x =; The defined global variable
alert (x);//
var g = eval ("x=");//eval resolves x according to the current context
To reference eval in the global scope, changing the value of the global scope without changing the value of the local scope
var g = eval; Global reference eval
var x = "global";//define global variable
(function f () {
var x = "local";
G ("x+= ' changed '");
alert (x);//local variable Locals
}) ();//iife Execute expression immediately
To change the value of a local variable in a local scope without changing the value of the global variable
var g = eval; Global reference eval
var x = "global";//define global variable
(function f () {
var x = "local";
Eval ("x+= ' changed '");
alert (x);//local variable localchanged
}) ();//iife immediate execution
of expression alert (x);//global variable's value global
Summary
Eval execution depends on the context to determine whether the variable is local or global, so using the Eval function, the key is to see the scope of the reference eval!
The above is a small set to introduce the JavaScript will know will be (v) eval use of relevant knowledge, I hope to help you, if you have any questions please give me a message, small series will promptly reply to everyone. Here also thank you very much for the cloud Habitat Community website support!