Example of JS dynamic call method name

Example of JS dynamic call method name

Many friends may not know how to dynamically call a method name in JS. The following is an example of how to call a method.

First, let's look at a function in JS.

 

JavaScript eval () function

Definition and usage

 

The eval () function computes a string and executes the JavaScript code.

Syntax

 

Eval (string)

 

Parameter description

 

String is 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.

 

Instance

 

Example 1

 

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

The Code is as follows:

<Script type = "text/javascript">

 

Eval ("x = 10; y = 20; document. write (x * y )")

 

Document. write (eval ("2 + 2 "))

 

Var x = 10

Document. write (eval (x + 17 ))

 

</Script>

 

Output:

 

200

4

27

 

Example 2

 

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

The Code is as follows:

Eval ("2 + 3") // returns 5

Var myeval = eval; // The EvalError may be thrown.

Myeval ("2 + 3"); // The EvalError may be thrown.

 

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

The Code is as follows:

Try {

Alert ("Result:" + eval (prompt ("Enter an expression :","")));

}

 

Catch (exception ){

Alert (exception );

}

 

The first method is to use eval in js

 

The following is an example of self-Writing

The Code is as follows:

Call ("showmsg ");

 

Function call (functionName ){

Eval ("this." + functionName + "()");

}

Function showmsg (){

Alert ("success ");

}

 

Eval can automatically recognize and call the concatenated string as a method.

 

But the downside is that someone can call any method by changing the name of the method you call.

 

The second method is mainly used as a custom method.

 

The second method requires specific writing methods.

The Code is as follows:

Function call (functionName ){

Showmsgs ["showmsg"] ();

}

 

Var showmsgs = {showmsg: function (){

Alert ("success ");

}

}

Call ("showmsg ");