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In-depth understanding of the use of JS function parameters (arguments)
In-depth understanding of the use of JS function parameters (arguments)
The parameters of JS functions can be obtained using the arguments object within the function.
There are two ways to call parameters:
1. Use of expected parameters.
2. Use of actual passed parameters.
Application example:
function Test(a, b){
var i, s = "Test函数有";
var numargs = arguments.length; // 获取实际被传递参数的数值。
var expargs = Test.length; // 获取期望参数的数值，函数定义时的预期参数个数（有a和b 2个参数）。
s += (expargs + "个参数。");
s += "\n\n"
for (i =0 ; i < numargs; i++){ // 获取参数内容。
s += " 第" + i + "个参数是：" + arguments[i] + "\n";
}
return(s); // 返回参数列表。
}
alert(Test('param1','second param','第三个参数'));It should be noted that:
arguments is an object object, it is not an array, and methods such as shift, push, and join cannot be used on it.
The i in arguments[i] used in the above example is only an attribute of the arguments object and cannot be understood as an array subscript.
Code Demonstration
<html>
<head>
<script language="javascript">
function reloadList(){
if(typeof arguments[0] == "function"){
arguments[0].call(this);
arguments[0]();
}
if(typeof arguments[0] == "string")
alert(arguments[0]);
if(typeof arguments[0] == "number")
alert(arguments[0]);
if(typeof arguments[0] == "undefined")
alert(arguments[0]);
if(typeof arguments[0] == "boolean")
alert(arguments[0]);
if(typeof arguments[0] == "null")
alert(arguments[0]);
}
reloadList(function(){});
</script>
</head>
<body>
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