Convert the function parameter arguments into an array in JavaScript.

1. Why is arguments not an array? How to prove it?

Arguments does not have array slice or other methods, so they are not of the array type.

Verification:

 
FunctionTestargs (){VaRArr = [1, 2, 3]; Console. Log (TypeofArguments. Slice); console. Log (TypeofArr. Slice);} testargs ();
 

Output:

 
UndefinedFunction
 

Of course, you can also prove it in other ways, such as viewing constructor.

2. How to convert to an array?

Use the Slice Method of array as follows:

FunctionArg2arr (){VaRArr =Array. Prototype. Slice. Call (arguments); console. Log (ARR);} arg2arr (1, 2, 3 );
 

Output: [1, 2, 3]

You can also write it as follows:

 
Array. Prototype. Slice. Call (arguments, 0)
 

3. How to use native js to implement your own Slice Method

Array. Prototype. Slice =Function(START, end ){VaRResult =NewArray (); Start= Start | 0; End= End |This. Length;//This points to the called object. When the call is used, the point of this can be changed, that is, to the passed object. This is the key.For(VaRI = start; I <end; I ++) {Result. Push (This[I]);}ReturnResult ;}
 

4. Is there a toarray method in JS? If not, how can I implement one by myself?

VaR Toarray = Function  (S ){  Try  {  Return  Array. Prototype. Slice. Call (s );}  Catch  (E ){  VaR Arr = [];  For ( VaR I = 0, Len = S. length; I <Len; I ++ ){ //  Arr. Push (s [I]); Arr [I] = s [I]; //  It is said that this is faster than push.  }  Return  Arr ;}}