3.6 Variadic Functions

>>>

function test() {
    return arguments;
}

>>>

test(1, 2, 3)

[1, 2, 3]

The special variable arguments contains all the function call arguments. It is an Array-like object that can be accessed like a normal Array.

>>>

function add() {
    var res = 0;
    for (var arg of arguments) {
        res += arg;
    }
    return res;
}

>>>

add(1, 2, 3, 4, 5)

Using the arguments array to create a variadic function (a function with variable number of arguments) is straight-forward.

>>>

function tail() {
    return arguments.slice(1);
}

>>>

tail(1, 2, 3)

TypeError: arguments.slice is not a function. (In 'arguments.slice(1)', 'arguments.slice' is undefined)

But take note. The arguments variable is only Array-like, it is not a proper Array object. So it lacks most of its methods and general niceness.

>>>

var tail2 = (...args) => args.slice(1);

>>>

tail2(1, 2, 3)

[2, 3]

The newer ...var rest parameters syntax (since ES6 in 2015) does away with the arguments variable. Instead, additional arguments are provided in a normal Array.

>>>

var tail3 = (first, ...others) => others;

>>>

tail3(1, 2, 3)

[2, 3]

The new syntax supports both declared and variable arguments. Of course, there can be only one rest parameter and it has to go at the end.

>>>

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