A brief discussion on the various definition methods and differences of js functions

There are generally three ways to define a function:

1. Function keyword (function) statement:

function fnMethodName(x){
alert(x);
}

2. Function literals (Function Literals):

var fnMethodName = function(x){ alert(x);}

3.Function() constructor:

var fnMethodName = new Function('x', 'alert(x);')

The above three methods define the same method function fnMethodName, The first is the most commonly used method. The latter two copy a function to the variable fnMethodName, and this function has no name, that is, an anonymous function. In fact, quite a few languages ​​have anonymous functions.

Examples are as follows:

【The first type - function keyword (function) statement】

<script type="text/javascript">
 
  function add(num1,num2)
    {
    return num1+num2+200;
    }
  var sum=add(122,10000);
  window.document.write(sum);
 
</script>

【The second type - function literals (Function Literals):】

<script type="text/javascript">
 
  var add=function(num1,num2)
    { return num1+num2+200;}
  var sum=add(122,300);
  window.document.write(sum);
</script>

【Chapter Three types of -Function() constructors:】

<script type="text/javascript">
    var add=new Function("num"," return num+200");//此时Function 这种方法用的比较少
    var sum=add(122);
    window.document.write(sum);
 
</script>

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