Javascript eval () function

ArticleDirectory

• Syntax
• Return Value
• Description
• Throw
• Example 1
• Example 2

Definition and usage

The eval () function can calculate a string and execute the JavascriptCode.

Syntax

 
Eval (string)
 

Parameters	Description
String	Required. The string to be calculated, which contains the Javascript expression to be calculated or the statement to be executed.

Return Value

Returns the string value (if any ).

Description

This method only accepts the original string as the parameter. If the string parameter is not the original string, this method will be returned without any change. Therefore, do not pass a String object as a parameter for the eval () function.

If you try to override the eval attribute or assign the eval () method to another attribute and call it through this attribute, ecmascript can throw an evalerror exception.

Throw

If the parameter does not contain valid expressions and statements, a syntaxerror exception is thrown.

If eval () is illegally called, an evalerror error is thrown.

If the JavaScript code passed to eval () generates an exception, Eval () will pass the exception to the caller.

Tips and comments

Tip:Although eval () is very powerful, it is rarely used in actual use.

Example 1

In this example, we will use eval () on several strings and look at the returned results:

<SCRIPT type = "text/JavaScript"> eval ("x = 10; y = 20; document. write (x * Y) ") document. write (eval ("2 + 2") var x = 10document. write (eval (x + 17) </SCRIPT>

Output:

200427

Example 2

In other cases, the results returned by eval () are as follows:

Eval ("2 + 3") // return 5var myeval = eval; // The evalerror myeval ("2 + 3") may be thrown; // The evalerror exception may be thrown

You can use the following code to check whether the eval () parameter is valid:

Try {alert ("Result:" + eval (prompt ("enter an expression:", "");} catch (exception) {alert (exception );}

Tiy

Eval ()