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eval Method (Visual Studio - JScript)

Updated: July 2009

Evaluates JScript code and executes it.

function eval(codeString : String [, override : String])

codeString

Required. A string that contains valid JScript code.

override

Optional. A string that determines which security permissions to apply to the code in codeString.

The eval function allows dynamic execution of JScript source code.

The code passed to the eval method is executed in the same context as the call to the eval method. Note that new variables or types defined in the eval statement are not visible to the enclosing program.

The code passed to the eval method is executed in a restricted security context, unless the string "unsafe" is passed as the second parameter. The restricted security context helps to prevent access to system resources, such as the file system, the network, or the user interface. A security exception is generated if the code attempts to access those resources.

When the second parameter of eval is the string "unsafe", the code passed to the eval method is executed in the same security context as the calling code. The second parameter is case sensitive, so the strings "Unsafe" or "UnSAfE" will not override the restricted security context.

Security noteSecurity Note:

Use eval in unsafe mode only to execute code strings obtained from trustworthy sources.

For example, the following code initializes the variable myDate to a test date.

var dateFn = "Date(1971,3,8)";
var myDate;
eval("myDate = new " + dateFn + ";");

print (myDate);

Date

History

Reason

July 2009

Modified example.

Content bug fix.

March 2009

Modified example.

Content bug fix.

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