JS Functions

Return “underfined” by default, possible to assign custom value using “return”.
How to pass parameters:

var post = {
    id: 1,
    title: 'Function Parameters'
};

var displayTitle = function( title ) {
    console.log( title );
};

displayTitle( post.title );

/********************************
 * A Function with Single Parameter
 * 1.2.21.1
 *
 *******************************/

// var post = {
//       id: 1,
//       title: 'Function Parameters'
//     };


// var displayTitle = function( title ) {

//   console.log( title );

// };

// displayTitle( post.title );





/********************************
 * Function Calls
 * with Different Parameters
 * 1.2.21.2
 *
 *******************************/

// var posts = [
//    {
//       id: 1,
//       title: 'Function Parameters'
//     },
//     {
//       id: 2,
//       title: 'Parameters are so flexible!'
//     }
//  ];


// var displayTitle = function( title ) {

//   console.log( title  );

// };

// for( var post of posts ) {

//   displayTitle( post.title );
  
// }


/********************************
 * Function w Multiple Parameters
 * And Multiple Function Calls
 * 1.2.21.3
 *
 *******************************/

// var title = 'Post about Parameters',
//     author = 'Zac',
//     recommendedPost = 'Learn JavaScript';


// var displayPost = function( title, author, recommendedPost ) {

//   console.log( title + ' by ' + author );
//   console.log( 'Read next: ' + recommendedPost );

// };

// displayPost( title, author, recommendedPost );




/********************************
 * Function w Multiple Parameters
 * And Multiple Function Calls
 * 1.2.20.1
 *
 *******************************/

// var post = {
//       id: 1,      
//       title: 'Post about Parameters'
//     },
//     author = {
//       id: 1,
//       displayName: 'Zac'
//     },
//     relatedPosts = [
//       'Learn JavaScript',
//       'JavaScript Functions',
//       'Multiple Parameters'
//     ];

// var displayTitle = function( title ) {
//   console.log( '<h2>' + title + '<h2>'  );  
// }

// var displayAuthor = function( author ) {
//   console.log( '<p>By: ' + author + '<p>'  );
// }

// var displayRelatedPosts = function( relatedPosts ) {

//   console.log( '<p>Related Posts</p>' );
//   console.log( '<ul>' );  
//   for ( var post of relatedPosts ) {
//     console.log( '<li>' + post + '</li>' );
//   }
//   console.log( '</ul>' );  
  
// }

// var displayPost = function( title, author, relatedPosts ) {

//   displayTitle( title );
//   displayAuthor( author );
//   displayRelatedPosts( relatedPosts );

// };

// displayPost( post.title, author.displayName, relatedPosts );

MDN Docs on functions

Function Return Examples