{JS} variable length parameter list: Arguments object

{JS} variable length parameter list: Arguments object
In a function, the identifier arguments has a special meaning. it is a special attribute that references the Arguments object. the Arguments object is an array-like object. You can obtain the parameter values passed to the function by subscript. the Arguments object also defines the callee attribute.

The Arguments object can be used in multiple aspects.
1. Check whether the real parameters are correct during function calling.
Function f (a, B ){
If (arguments. length! = 2 ){
Throw new Error ("the function expects two parameters ");
}
// Todo:
}

2. Compile variable parameter functions
Function max (/*...*/){
Var m = Number. NEGATIVE_INFINITY;
For (var I = 0; I <arguments. length; I ++ ){
If (arguments [I]> m ){
M = arguments [I];
}
}
Return m;
}

Var largest = max (3, 5,100, 88, 99, 11,100 );

3. the Arguments object has an extraordinary feature. when a function has a named parameter, the array element of the Arguments object is a synonym for storing the local variables of the function parameter. arguments [] arrays and named parameters are two different methods that reference the same variable. changing the value of a parameter using the parameter name also changes the value obtained through the arguments [] array. changing the parameter value through the arguments [] array also changes the parameter value obtained using the parameter name. for example:
Function f (){
Console. log ();
Arguments [0] = null;
Console. log ();
}

F (1 );

4. finally, remember that arguments is just a common JS tag, not a reserved word. if a parameter or local variable in the function uses this name, it hides the reference to the Arguments object. for example:
Function e (){
Var arguments = 1; // hide a reference to the Arguments object
Console. log (arguments );
}

Function f (){
Console. log (arguments); // still points to the reference of the Arguments object
Var arguments = 1;
}

Function g (arguments) {// hide a reference to the Arguments object
Console. log (arguments );
}

E (1, 2 );
F (1, 2 );
G (1, 2 );

Therefore, it is best to use arguments as a reserved word and avoid using it as a variable name.

By bill200711022