Javascript eval()用法及代码示例

eval()是全局对象的函数属性。

• eval()函数的参数为​​字符串。
• 如果字符串表示一个表达式，则eval()评估该表达式。如果参数代表一个或多个JavaScript语句，则eval()将评估这些语句。
• 我们不调用eval()来评估算术表达式； JavaScript自动评估算术表达式。

用法:

eval(string)
参数：
String:
A string representing a JavaScript expression, statement, or 
sequence of statements. The expression can include variables 
and properties of existing objects.

返回值：
The completion value of evaluating the given code is 
returned by using eval(). 
If the completion value is empty, undefined is returned. 

例子：

Input:eval(new String('2 + 2'));
Output:returns a String object containing "2 + 2"

Input:eval(new String('4 + 4'));
Output:returns a String object containing "4 + 4"

下面的程序将说明eval()的用法：函数更深入：程序1：

<script> 
    // JavaScript to illustrate eval() function 
    function func() { 
  
        // Original string 
        var a = 2; 
        var b = 2; 
  
        // Finding the sum 
        var value = eval(new String(a + b)); 
        document.write(value); 
    } 
// Driver Code 
func(); 
< /script>                    

输出：

4

程序2:：

<script> 
    // JavaScript to illustrate eval() function 
    function func() { 
  
        // Original string 
        var a = 4; 
        var b = 4; 
  
        // Finding the multiplication 
        var value = eval(new String(a * b)); 
        document.write(value); 
    } 
// Driver code 
func(); 
< /script>                    

输出：

16