oop - JavaScript Functional Classes -

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i learning object oriented programming in javascript udacity course. know among below best technique create functional object , why.

first code:

var car = function(loc){     var obj = {loc:loc};     extend(obj, car.methods);     return obj; }  car.methods = {     move: function(){         this.loc++;     } };

second code:

isnt above code same as:

var car = function(loc){     var obj = {loc:loc};     obj.move= function(){         this.loc++;     }     return obj; }

third code

var car = function(loc){     var obj = {loc:loc};     obj.move=move;     return obj; }  move=function(){     this.loc++; };

i want know, style of coding 1 should follow. understand third code better second because more instances of functions created whenever use car function. doesn't first code create more instance of same function?

thanks in advance.

answer: none of above. try this:

function car(loc) {     this.loc = loc; }  car.prototype.move = function () {     this.loc++; };  var obj = new car(someloc);  obj.move();

this uses object prototyping javascript's implementation of object-oriented programming. can read more prototypes , inheritance here on mdn.

the reason why preferred method because organizes code lot better, , object can identified car using instanceof. i'll extend example below demonstrate properties of inheritance:

// vehicle constructor  function vehicle(wheels, speed, loc) {      this.wheels = wheels;      this.speed = speed;      this.loc = loc;  }    // instance method move  vehicle.prototype.move = function () {      this.loc += this.speed;  };    // car constructor  function car(loc) {      // js equivalent of super()      vehicle.call(this, 4, 60, loc);  }    // override instance method move  car.prototype.move = function () {      this.loc++;  };    // make car inherit vehicle  car.prototype.__proto__ = vehicle.prototype;    // construct instance of car loc of 0  var obj = new car(0);    // obj instance of vehicle...  if (obj instanceof vehicle) {      console.log('wheels: %d', obj.wheels); // 4      console.log('speed: %d', obj.speed); // 60      console.log('loc: %d', obj.loc); // 0  }    // ...and instance of car  if (obj instanceof car) {      obj.move();      console.log('loc: %d', obj.loc); // 1, not 60  }

this demonstrates how can use prototype chain override instance methods, , how inheritance allows obj instance of both car , vehicle. hope can see why using prototype chain preferred method.


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