Saturday, February 16, 2013

TypeScript - The rest parameter

Rest parameter in TypeScript has nothing todo with REST (REpresentational State Transfer)

If you are familiar with C# params keyword, The rest parameter is the same. The rest parameter lets you specify a function parameter that takes an argument where the number of arguments is variable.

An example could be a function that make a Sum of a variable length of numbers:


Sum(1,2,3,4);

C# example

public int Sum(params int[] list)
{
  int sum = 0;
  foreach (int i in list)
    sum += i;
  return sum;
}
TypeScript example

public Sum(...list Number[]) : number
{
    return list.reduce( 
        (a,b) => { a + b }
    );
}
And the result when compiled to JavaScript

function sum() {
    var numbers = [];
    for (var _i = 0; _i < (arguments.length - 0); _i++) {
        numbers[_i] = arguments[_i + 0];
    }
    return numbers.reduce(function (a, b) {
        return a + b;
    });
}


1 comment:

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