It’s a way of pulling out user specified values, ie function (a, b, … rest) {return rest} Whoever provides the arguments always provides a and b, but they can also give the function optional arguments and any of those are captured with the rest parameter More on reddit.com

As for example 1, you are right. Its called a "rest parameter". Each parameter will be an element in the array. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/rest_parameters

'arguments' is an array-like object that contains everything passed into a function, whether they were included in the declaration or not. It is better to use a rest parameter. In general, it's usually better to be explicit. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Functions/arguments

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Because you're severely limiting the re-use potential if you only define variables outside of the function var a = 5; var b = 10; function add () { return a + b; } add(); // 15 add(); // 15 add(); // 15 This function will only ever return the sum of a + b, and to change the sum, you need to change the values of a and b. Changing those values directly only works in very small code blocks. In more complicated situations, you may not even be able to reach those values because of scope limitations. function add (a, b) { return a + b; } add(5, 10); // 15 add(1, 11); // 11 add(3.14, 12); // 15.14 Now I have a function that I can call from anywhere and which performs a simple operation. While add is obviously incredibly basic, code can become far more complex and yet the fundamental lesson still applies: parameters make a function re-usable and unique for each set of arguments passed to it. You can still use external variables as well var a = 5; function add (b, c) { return a + b + c; } add(5, 10); // 20 a = 20 add(5, 10); // 35 But you need to be careful about the interactions it can cause when your code changes in unexpected ways. More on reddit.com

variadic functions

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