14-Functions.md

Episode 14 : First class and Anonymous functions

(there is no Episode 13 idk why lol)

Function statement : Just your normal function definition

function a() {
  console.log("a called");
}
a();

Function Expression : Assigning a function to a variable. Function acts like a value

var b = function() {
  console.log("b called");
}
b();

Difference btw function statement and expression is Hoisting

• You can put "a();" before "function a()" and it will still work. But putting "b();" before "var b = function()" throws a typeError.
• Why? During mem creation phase a is created in memory and function assigned to a. But b is created like a variable (b:undefined) and until code reaches the function() part, it is still undefined. So it cannot be called.

Function Declaration : Exactly same as function statement

Anonymous Function : A function without a name

• They don't have their own identity. So an anony function without code inside it results in an error.
• Anony functions are used when functions are used as values eg. the code sample for function expression above

Named Function Expression : Same as Function Expression but function has a name instead of being anonymous

var b = function xyz() {
  console.log("b called");
}
b(); // prints "b called" properly
xyz(); // Throws ReferenceError:xyz is not defined.

xyz function is not created in global scope. So it can't be called.

Parameters vs Arguments

var b = function(param1, param2) {  // labels/identifiers that get the arg values 
  console.log("b called");
}
b(arg1, arg2); // arguments - values passed inside function call

First Class Function aka First Class Citizens

• You can pass functions inside a function as arguments(WOW!)

var b = function(param1) {
  console.log(param1); // prints " f() {} "
}
b(function(){
  
});

this can also be done:

var b = function(param1) {
  console.log(param1);
}
function xyz(){

}
b(xyz); // same thing as prev code

you can return a function from a function:

var b = function(param1) {
  return function() {
  
  }  
}
console.log(b()); //we log the entire fun within b. 

Arrow Functions (latest in ES6 (ECMAScript 2015) -> coming in future lecture