Almost! Both take a string as input and return a number. But one returns an integer and the other a float. So parseInt("3.14") returns 3 and parseFloat("3.14") returns 3.14

Functions are very cool. We're all used to variables that contain unknown values:

    let x = prompt("enter your age", 18);
    let y = x + 1;
    alert("Next year, you will be "+y);

(I made a mistake above; what is it?)

In the above code, we know what all the functions are. But that might not be the case in another situation, where the variable holds a function.

    function doSomething(seq, fn) {
        return seq.map(fn);
    }
    function square(x) {
        return x*x;
    }
    console.log(doSomething([1,2,3], square));
    console.log(doSomething([1,2,3], x => x*x*x));

For fun, here's the same idea in Python:

def do_something(seq, fn):
    return [ fn(x) for x in seq ]

def square(x):
    return x**2

print(do_something(range(5), square))

print(do_something(range(5), lambda x: x**3))

When we are going to pass a function to someone else to run, often we don't need a name for it. So, we just give the code: an anonymous function.

After all, the only reason to have a name is to refer to something later.

Yeah, they are, aren't they? Very concise in some cases (see above). There are some subtle differences, which we'll talk about later. But essentially:

function name(a, b) { return expr(a,b) ; }

Is the same as

(a, b) => expr(a,b)

You omit the name, if any, the return keyword and the braces.

But you can add the braces and return back if you need them.

forEach is a method on arrays that takes a function and invokes it for each element of the array. It returns no value. We can use it instead of a loop. (Loops also return no value.)

It's not necessarily preferred in industry, but for this class, I do. Because:

• It helps us practice with functions as arguments
• It transfers to other coding techniques, such as Map-Reduce

I'm not sure what you mean by "looping through functions". Do you mean the forEach method? We will do some practicing with that.

Sorting is similar to Python, but a little different. In Python:

y = [1, 8, 4, 16, 25 ]

print(sorted(y))
print(sorted(y, key = lambda n: str(n)))
print(sorted(y, key = lambda n: str(n), reverse = True))

In JavaScript, we provide a comparison function between any two elements:

var x = [3, 5, 7, 9, 11];
var y = x.map(n => n*n);
y.sort()
y.sort( (a,b) => a-b )
y.sort( (a,b) => b-a )

The comparison function must return *negative* if a should precede b, otherwise *positive*, and *zero* for ties.

Glad to hear it!