JavaScript Functions #

Minimum Viable Example #

As simple as it gets:

function someFunctionName(some_parameter) {
    ...;
    return some_variable_defined_above; 
}

// console.log(someFunctionName(argument_of_some_sort))
// ^ does whatever the function says to do to the argument provided for the parameter

^ parameters can be empty.

Function can be called with:

someFunctionName();

Arguments #

Things to know about parameters and their arguments:

• Order matters

• Default values can be provided (function someFunction(some_arg = 'default value') { ... })

• Functions can take other functions as parameters (see higher order functions).

Helper Functions #

Helper functions: functions called within other functions.

function firstFunction(some_arg) {
    ...;
    return some_var;
}

function secondFunction(another_arg) {
    ...;
    return firstFunction(another_arg);
}

secondFunction(...);

Function Expression #

Related to anonymous functions (function with no name).

Function expression is a mash-up of variables and functions. Convention is to invoke with a const.

const someVar = function(param1, param2) {
    ...;
    return some_value;
}

someVar(arg1, arg2)

Hoisting is not allowed with function expressions (see below for hoisting).

Arrow Functions #

Replace function statement with a fat arrow => to create a function.

Start with parameters.

const some_function = (param1, param2) => {
    ...;
    return some_value;
}

Concise Body Arrow Functions #

A more condensed form of arrow functions.

If there’s just exactly one parameter, () are not required.

const some_var = some_param => {};

If the function body can fit on one line, {} and return are not required.

const some_var = some_param => some_param * some_param; // arbitrary operation in this example

Renaming #

Functions can easily be renamed.

const newName = oldName; // no parentheses

newName(); // just a reference to the original function

Hoisting #

Ability to call a function before it’s defined. Generally not recommended.

someFunctionName();

function someFunctionName(some_arg) {
    ...;
}

Properties #

.name gets the function’s original name

console.log(someFunction.name)