VARIADIC FUNCTIONS IN JAVASCRIPT

KERALA JS USER GROUP MEETUP - SEPT 2014

Variadic What?

In computer programming, a variadic function is a function of indefinite arity, i.e., one which accepts a variable number of arguments.

- Wikipedia

The best example!


 #include <stdio.h>

 int main(){
   printf("Hello world!");
   return 0;
 }


 #include <stdio.h>

 int main(){
   printf("Hello world! \n %d + %d = %d", 1, 2, 1+2);
   return 0;
 }

Function Arguments

 var concat = function(arg) {
   return arg;
 }

 concat();
 //=> undefined

 concat('Hi There!');
 //=> 'Hi There!'

 concat('Hi There', 'Hi There Again');
 //=> 'Hi There!'

Arguments Object

The arguments object is an Array-like object corresponding to the arguments passed to a function.

- MDN JavaScript Reference

...


 var whatAreTheParameters = function() {
   return arguments;
 }

 whatAreTheParameters()
 //=> []

 whatAreTheParameters(1)
 //=> [1] 

 whatAreTheParameters(1, 'two', 3.0)
 //=> [1, 'two', 3]

Concat Function


 var concat = function() {
    var result = '';
    
    for(var i=0; i < arguments.length; i++)
      result += arguments[i];

    return('' == result ? undefined : result);
 }

 concat('Hello ', 'world');
 //=> 'Hello world!'

List Function


  var list = function(type) {
    var result = '<' + type + 'l><li>';
    var args = Array.prototype.slice.call(arguments, 1);
    result += args.join('</li><li>');
    result += '</li></' + type + 'l>';
  
    return result;
  }

  list('u', 'one', 'two');
  //=> '<ul><li>one</li><li>two</li></ul>'

ECMAScript 6

Rest Parameters


  var list = function(type, ...args) {
    var result = '<' + type + 'l><li>';
    result += args.join('</li><li>');
    result += '</li></' + type + 'l>';
  
    return result;
  }

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters

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