How does an anonymous function know what function to do?

Question

I'm working in JS and the DOM. We just wrote a function and then turned it into an anonymous function. In the original function we use the function "say" as the first parameter and the argument "Hello" as the second. When we finished with the anonymous function it no longer had the word say in the syntax, so how does the function know to say what is passed as the argument? How would you do this if you changed your mind and wanted it to do a different function? This seems pretty mysterious to me at the moment.

Answer 1 · 2017-02-06T16:10:44Z

February 6, 2017 4:10pm

The function doesn't need a name. When you call the function all the code inside the curly brackets is executed.

The function is probably assigned to a variable and when it's used the function is called and the code gets executed.

The function knows what to do because it just executes the code inside it, like "saying" hello. Printing it to the console or placing it in the HTML on the page.

Answer 2 · 2017-02-06T16:29:04Z

February 6, 2017 4:29pm

Don't think that an anonymous functions are reusable. They are used as a regular value is. You pass them into functions like plain old numbers and strings do. They are just for representing blocks of code, and not meant to be reusable.

However, if you give them a name, they can be reusable.

They are so much like plain old values that you can even assign a variable to it and that's the same as defining a function the way you are used to:

var sayHello = function () {
    document.write("Hello");
}

// The line above is THE SAME AS the line below

function sayHello () {
    document.write("Hello");
}

// The lines above are also THE SAME AS the one below

var sayHello = () => {
    document.write("Hello");
}

In fact, You van even create a regular reusable function and pass it in to a DOM function:

var element = document.getElementById("someElement");

function sayHello () {
    document.write("Hello");
}

element.addEventListener('mouseover', sayHello);

I hope this helps. ~Alex

Welcome to the Treehouse Community

Looking to learn something new?

S Ananda

S Ananda

How does an anonymous function know what function to do?

2 Answers

Robin van Loon

Robin van Loon

Alexander Davison

Alexander Davison