JavaScript: Flexible Arguments



In many use-cases it's very useful to know total number of in-parameter and there type of param.

function testArgs(){
 var args = arguments,
 param = args[0],
 type = Object.prototype.toString.call(param);
 console.log('total number of in param: '+args.length);
 console.log('type of first param: '+type);
}
-> testArgs('test');
//ans:
//total number of in param: 1
//type of first param: [object String]
-> testArgs(3, 3);
//ans: 
//total number of in param: 2
//type of first param: [object Number]


Above function will print the number of parameter pass to it and first parameter type.
Jquery use this trick to deal with optional parameter (like. jQuery.extend, jQuery.when etc.)

Few more example on this concept.
##Add function with flexible argument
function add(){
 var total = 0,
  arg = arguments;
 for(var i =0; i< arg.length; i++){
  total += arg[i];
 }
 return total;
}
->add(1, 2, 5, 22); //ans: 30
->add(1, 2); //ans: 3

##find n highest number from the array
function highest(){ 
 function makeArray(array){ 
  //Arrays have .slice and .splice methods which return new arrays.
  return Array().slice.call( array );
 } 
 return makeArray(arguments).slice(1).sort(function(a,b){ 
  return b - a; 
 }); 
}
->highest(1, 1, 2, 3)[0]; //1st highest ans: 3
->highest(3, 1, 2, 3, 4, 5)[1]; //2nd highest ans: 4



John Resig wrote a function for method overloading and he is using "arguments.length" to identify which function have to call
link of original post
// addMethod - By John Resig (MIT Licensed)
function addMethod(object, name, fn){
    var old = object[ name ];
    object[ name ] = function(){
        if ( fn.length == arguments.length )
            return fn.apply( this, arguments );
        else if ( typeof old == 'function' )
            return old.apply( this, arguments );
    };
}

//how to use it with function
function Users(){
  addMethod(this, "find", function(){
    // Find all users...
  });
  addMethod(this, "find", function(name){
    // Find a user by name
  });
  addMethod(this, "find", function(first, last){
    // Find a user by first and last name
  });
}

//how to use with object prototype
function Users(){}
addMethod(Users.prototype, "find", function(){
  // Find all users...
});
addMethod(Users.prototype, "find", function(name){
  // Find a user by name
});
addMethod(Users.prototype, "find", function(first, last){
  // Find a user by first and last name
});


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