eval is doing what?

eval () action:

JS parsed into the string parameter code and run, and returns the execution result;

E.g:

the eval ( " 2 +. 3 " ); // performs its operation and returns the computed value. 
the eval ( " var age = 10 " ); // declare a variable age

eval scope

A function () { 
   the eval ( " var X =. 1 " ); // equivalent. 1 = X var; 
   the console.log (X); // output. 1 
} 
A (); 
the console.log (X); // error x is not defined

Description Scope effective in all its range of content

Example 2:

A function () { 
   window.eval ( " var X =. 1 " ); // equivalent to window.x = 1; defines global variables 
   the console.log ( " X " ); // output. 1 
} 
A (); 
the console.log (X); // output 1

This code tragedy? IE8 in IE8 and what version is not supported.

Solution:

functionA () {
  IF (window.execScript) { // support IE8 and below versions 
  window.execScript ( " var X =. 1 " ); 
 } 
 the else { // conventional browsers support 
  window.eval ( " var X = . 1 " ); 
 } 
 the console.log (X); 
} 
A (); 
the console.log (X);

Precautions

You should avoid using eval, insecurity, huge performance (2 times, once parsed into js statement, once executed).

Other action

JSON string into a JSON object can be used when eval, for example:

var json ="{name:'Mr.CAO',age:30}";
var jsonObj = eval("("+json")");
console.log(jsonObj);

Guess you like