Question on Javascript Function Parameters

Question

I was trying to write some javascript function and realised that

function testFunction(input_1, input_2, input_3) {        alert("alert"); } 

however when i call the function like this:

<input type="button" value="click" onclick="testFunction("1", "2")"> 

why will it still work even with just two parameters?

Answer 1

You can call a Javascript function with any number of parameters, regardless of the function's definition.

Any named parameters that weren't passed will be undefined.

Extra parameters can be accessed through the arguments array-like object.

Answer 2

It doesn't actually matter how many parameters you are providing. the function interprets them and creates the arguments object (which acts as an array of parameters). Here's an example:

function sum(){    if(arguments.length === 0)        return 0;    if(arguments.length === 1)        return arguments[0];    return arguments[0] + sum.apply(this, [].slice.call(arguments, 1)); } 

It's not the most efficient solution, but it provides a short peak at how functions can handle arguments.