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Re: Why is eval( "05" ) a direct eval call in ECMAScript?

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  Re: Why is eval( "05" ) a direct eval call in ECMAScript? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2017-01-06 00:20 +0100

#32116 — Re: Why is eval( "05" ) a direct eval call in ECMAScript?

Stefan Ram wrote:

>   I am going to try to deduce why »eval( "05" )« is a
>   direct call of eval in ECMAScript. […]

Because you are not using the return value of eval().

There are syntactical *and* a functional differences between each of the 
following statements:

(function () {
  var v = 42;

  /* Modifies the local v;
     creates global “v” property if “v” cannot be resolved */
  eval("v = 23;");

  console.log(v);
}());

(function () {
  "use strict";

  var v = 42;

  /* Modifies the local v;
     throws ReferenceError if “v” cannot be resolved */
  eval("v = 23;");

  console.log(v);
}());


(function () {
  var v = 42;

  /* Modifies the local v; can declare the local v if not declared */
  eval("var v = 23;");

  console.log(v);
}());

(function () {
  "use strict";

  var v = 42;

  /* Declares and modifies the eval v, not the local v */
  eval("var v = 23;");

  console.log(v);
}());


(function () {
  var v = 42;

  /* Modifies the local v and x;
     create global “v” property if “v” cannot be resolved */
  var x = eval("v = 23;");

  console.log(v);
}());

(function () {
  "use strict";

  var v = 42;

  /* Modifies the local v and x;
     throws ReferenceError if “v” cannot be resolved
   */
  var x = eval("v = 23;");

  console.log(v);
}());


(function () {
  var v = 42;

  /* Redeclares and modifies the local v */
  var x = eval("var v = 23;");

  console.log(v);
}());

(function () {
  "use strict";

  var v = 42; 

  /* Declares and modifies the eval v, not the local v */
  var x = eval("var v = 23;");

  console.log(v);
}());


Also, in your case the code does not work in strict mode because "05" is an 
octal integer literal (produced by /OctalIntegerLiteral/):

| > eval("05")
| 5
| 
| > (function () { "use strict"; eval("05"); }());
| Uncaught SyntaxError: Octal literals are not allowed in strict mode.(…)
| 
| > (function () { var x = eval("05"); }());
| undefined
| 
| (function () { "use strict"; var x = eval("05"); }());
| Uncaught SyntaxError: Octal literals are not allowed in strict mode.(…)
| 
| > navigator.userAgent
| "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) 
| Chrome/53.0.2785.143 Safari/537.36"

(That is V8 JavaScript 5.3.332.47, see <chrome://version/>)

-- 
PointedEars
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