difference between function(d) and function(d,i)?

Question

Every D3js beginner must be going through this thought, I am pretty much sure about it.

I have been around this thing for few hours now!!!!But I don\'t

Answer 1

If you're talking about the callback functions you would pass to methods like .attr(), then the function is called for each item in the current selection, where the i gives you the index of the current item, but depending on what you're doing you might not care about the index. So although D3.js will always call your function with both arguments, if you don't actually need the second argument in a particular case your function need not declare it explicitly.

JavaScript lets you call any function with any number of arguments regardless of how many were explicitly included in the function declaration. If you call a function with fewer arguments than were defined the leftovers will get the value undefined. If you call a function with more arguments than were defined you can still access the additional ones from within the function by using the arguments object - or you can ignore them.

(Note: you should have a lowercase f in function().)