Functional Programming in JavaScript Notes (Array map & filter)

Categories: JavaScript; Tagged with: JS; @ November 20th, 2014 23:35

Array.Map:

Array.prototype.map = function(projectionFunction) {
     var results = [];
     this.forEach(function(itemInArray) {
        // ------------ INSERT CODE HERE! ----------------------------
         // Apply the projectionFunction to each item in the array and add
         // each result to the results array.
         // Note: you can add items to an array with the push() method.
         // ------------ INSERT CODE HERE! ----------------------------
     results.push(projectionFunction(itemInArray));
    });
    return results;

};
// JSON.stringify([1,2,3].map(function(x) { return x + 1; })) === '[2,3,4]'

Array.filter

Array.prototype.filter = function(predicateFunction) {
     var results = [];
     this.forEach(function(itemInArray) {
         // ------------ INSERT CODE HERE! ----------------------------
         // Apply the predicateFunction to each item in the array. If the
         // result is truthy, add each result to the results array.
         // Note: remember you can add items to the array using the array's
         // push() method.
         // ------------ INSERT CODE HERE! ----------------------------
     if(predicateFunction(itemInArray)) {
        results.push(itemInArray);
     }
     });
    return results;

};
// JSON.stringify([1,2,3].filter(function(x) { return x > 2})) === "[3]"

Chaining call

function() {
     var newReleases = [
             {
                 "id": 70111470,
                 "title": "Die Hard",
                 "boxart": "http://cdn-0.nflximg.com/images/2891/DieHard.jpg",
                 "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                 "rating": 4.0,
                 "bookmark": []
             },
             {
                 "id": 654356453,
                 "title": "Bad Boys",
                 "boxart": "http://cdn-0.nflximg.com/images/2891/BadBoys.jpg",
                 "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                 "rating": 5.0,
                 "bookmark": [{ id:432534, time:65876586 }]
             },
             {
                 "id": 65432445,
                 "title": "The Chamber",
                 "boxart": "http://cdn-0.nflximg.com/images/2891/TheChamber.jpg",
                 "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                 "rating": 4.0,
                 "bookmark": []
             },
             {
                 "id": 675465,
                 "title": "Fracture",
                 "boxart": "http://cdn-0.nflximg.com/images/2891/Fracture.jpg",
                 "uri": "http://api.netflix.com/catalog/titles/movies/70111470",
                 "rating": 5.0,
                 "bookmark": [{ id:432534, time:65876586 }]
             }
         ];
    // ------------   INSERT CODE HERE!  -----------------------------------
     // Chain the filter and map functions to select the id of all videos
     // with a rating of 5.0.
    return newReleases.
         filter(function(video) {
             return video.rating === 5.0;
         }).
         map(function(video) {
             return video.id;
         });
     // ------------   INSERT CODE HERE!  -----------------------------------

}

JavaScript Day1: Java Script Objects <-> IntelliJ 14 Jetty integration