What's wrong with javaScript's addition?

You define the function to accept three arguments and you are passing only one argument. As a result, the values of b and c are undefined in the function and adding undefined to a number results in NaN. Try this instead:

add(10, 10, 10); 

You need to pass your arguments separately:

add(10, 10, 10); 

The problem is that you've added the numbers before passing them to your function:

add(10+10+10); 

adds together 10, 10 and 10, then passes it to the function, so really your code is:

function add(a,b,c) { z= a+b+c; console.log(z); } add(30); 

Which will not work, because your function expects 3 arguments and only gets 1.

function add(a,b,c) { // a is 30, b and c are both undefined z= a+b+c; console.log(z); } 

Add function expects 3 parameters. a, b and c. What you are doing now is passing an expression 10+10+10 which is not a valid number. Try as following

function add(a,b,c) { z= a+b+c; console.log(z); } add(10,10,10);