JavaScript Prototype function Issue

Question

I have built a Constructor and added 3 functions to its prototype. When I try to call a function from the prototype i get this error

TypeError: undefined is not a function (evaluating 'fireOne.addLogs(8)')

Please can someone tell me what I am doing wrong. I cannot figure it out.

Thanks in advance

 function SignalFire(ID, startingLogs){
   this.fireID = ID;
   this.logsLeft = startingLogs;
 }


 var fireOne = new SignalFire(1, 20);
 var fireTwo = new SignalFire(2, 18);
 var fireThree = new SignalFire(3, 24);




 SignalFire.prototype = {

   addLogs: function(numLogs){
     this.logsLeft += numLogs;
   },


   lightFire: function(){
     alert("Whoooooosh!");
   },

   smokeSignal: function(message) {
     if (this.logsLeft < this.message.length / 10){
       alert("Not enough fuel to send " +
       "the current message!");
     }

     else {
       this.lightFire();
       var x = this.message.length;
       for(var i = 0; i < x; i++){
         alert("(((" + this.message[i] + ")))");
         if (i % 10 === 0 && i !== 0){
           this.logsLeft--;
         }
       }
     }
   }

 };

 fireOne.addLogs(8);

This would even work if you added them one by one (SignalFire.prototype.addLogs = function ...). But since you're outright replacing the entire prototype object, the reference is broken. — deceze
– deceze ♦, Commented Dec 1, 2016 at 14:02
Just create your objects right before your fireOne.addLogs(8) — user2085143
– user2085143, Commented Dec 1, 2016 at 14:03
It is the order of your code. You create before you add the prototype. put the var fireXXX = new SignalFire() after the prototype object... — epascarello
– epascarello, Commented Dec 1, 2016 at 14:18

epascarello · Accepted Answer · 2016-12-01 14:21:01Z

1

Problem is order of your code. You add things after it is created. If you add the prototype before you create the fires it will work.

function SignalFire(ID, startingLogs){
   this.fireID = ID;
   this.logsLeft = startingLogs;
 }

 SignalFire.prototype = {
    addLogs: function(numLogs){
     this.logsLeft += numLogs;
     console.log(this.logsLeft);
   }
 };

 var fireOne = new SignalFire(1, 20);
 fireOne.addLogs(8);

answered Dec 1, 2016 at 14:21

epascarello

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