JavaScript work must Know (v) use of eval

Eval

Eval (parse) Parse: Inside with the argument string, we know that executing JavaScript will compile execution,

to change the value of a global variable:

　　　　　　

        var x = 2; Defines the global variable        alert (x),//2        var g = eval ("x=3"), and//eval resolves x alert (x) based on the current context        ;//3

referencing eval at 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 locally        });//iife immediately executes        the expression alert (x);//The value of the global variable globalchanged

　　Reference changes the value of a local variable within 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 immediately executes an expression        alert (x);//global variable Value

Summary

Eval execution will determine whether the variable variables are local or global depending on the context, so using the Eval function is the key to seeing the scope of the reference eval!

JavaScript work must Know (v) use of eval