Definitions

Function declarations begin with the function keyword and are followed by three components:

  1. An identifier (...or name), which becomes a variable in which the newly defined function object is stored. The identifier is required in a named function declaration, but can be excluded for anonymous functions and function expression definitions (more on these later).

  2. A pair of parentheses (()). These store a comma-separated list of named function parameters.

  3. A pair of curly braces ({}). This is the body of the function, and stores zero or more JavaScript statements which will be executed when the function is invoked.

// function declaration
function greet(name) {
  return 'Hello ' + name;
}

// function invocation
greet('Dave'); // 'Hello Dave'

Declaring a named function with the function keyword creates a variable in the current scope. For example:

function foo(){}

foo is now a variable in the current scope. The value of the foo variable is function(){}.

Alternatively, you can explicitly store a function into a variable:

let bar;

bar = function foo(){};

The variable bar now contains the function function(){} as a value.

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