'undefined' result for variable in Javascript function

Question

something in my code is meaning that I am getting an array printed which contains only undefined values, not the random numbers I am expecting.

My code is below:

function List(max, min, numLists, numItems) {
    this.max = max,
    this.min = min,
    this.numLists = numLists,
    this.numItems = numItems,
    this.generateLists = function () {
        var fullArray = [];
        var completeArray = [];

        for (i = this.min; i < this.max; i++) {
            fullArray.push(i);
        }
        for (i = 0; i < numItems; i++) {
            var randomItem = Math.floor(Math.random() * (1 + (this.max - this.min)));
            completeArray.push(fullArray[randomItem]);
        }

        console.log(completeArray);
    }
}

var newList = new List(12, 100, 1, 15);

newList.generateLists();

The code is supposed to print a random list of number between the min and max values. I'm getting an array with 15 values in, but they are all undefined. I'm guessing this mean there is something wrong with my first 'for' loop?

If anyone has any suggestions on how I could make this better please do criticise!

Thanks in advance.

Joseph Marikle · Accepted Answer · 2016-10-26 14:54:28Z

1

You have min and max mixed up in your arguments list. this results in an impossible boundary for your numbers (greater than 100 but less than 12). Just swap the parameters in the first line from max,min to min,max.

function List(min,max,numLists,numItems){
    this.max = max,
    this.min = min,
    this.numLists = numLists,
    this.numItems = numItems,
    this.generateLists = function (){
        
        
        var fullArray = [];
        var completeArray = [];
        
        for ( i = this.min ; i<this.max ; i++) {
            fullArray.push(i);
            }
      
        for ( i = 0 ; i<numItems ; i++) { 
            var randomItem = Math.floor(Math.random() * (1+(this.max-this.min)));
            completeArray.push(fullArray[randomItem]);
            }
            
        console.log(completeArray);
        
        }
}
        
var newList = new List ( 12 , 100 , 1,15);

newList.generateLists();

answered Oct 26, 2016 at 14:54

Joseph Marikle

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1 Comment

Wormdog1 Over a year ago

This was it, doh! Thanks

Charles Guo · Accepted Answer · 2016-10-26 15:31:45Z

1

I think you swap the position of max and min when you initiate newList.

Change the line to:

var newList = new List ( 100, 12 , 1,15);

Then it should work fine.

edited Oct 26, 2016 at 15:31

answered Oct 26, 2016 at 15:02

Charles Guo

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Comments

Weedoze · Accepted Answer · 2016-10-26 14:52:37Z

0

You were pushing fullArray[randomItem] that contains nothing. It is never initialized

function List(max, min, numLists, numItems) {
  this.max = max,
    this.min = min,
    this.numLists = numLists,
    this.numItems = numItems,
    this.generateLists = function() {


      var completeArray = [];

      for (i = 0; i < numItems; i++) {
        var randomItem = Math.floor(Math.random() * (1 + (this.max - this.min)));
        completeArray.push(randomItem);
      }

      document.write(completeArray);

    }
}

var newList = new List(12, 100, 1, 15);

newList.generateLists();

answered Oct 26, 2016 at 14:52

Weedoze

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Comments

Lew · Accepted Answer · 2016-10-26 14:56:39Z

I think maybe you max and min arguments were in the wrong order. You were trying to access the fullArray with a negative index due to subtracting a larger number from a smaller one.

function List(min,max,numLists,numItems){
    this.max = max,
    this.min = min,
    this.numLists = numLists,
    this.numItems = numItems,
    this.generateLists = function (){
        
        
        var fullArray = [];
        var completeArray = [];
        
        for ( i = this.min ; i<this.max ; i++) {
            fullArray.push(i);
            }
        for ( i = 0 ; i<numItems ; i++) { 
            var randomItem = Math.floor(Math.random() * (1+(this.max-this.min)));
            console.log(randomItem)
            completeArray.push(fullArray[randomItem]);
            }
            
        console.log(completeArray);
        
        }
}
        
var newList = new List ( 12 , 100 , 1,15);

newList.generateLists();

Alex González · Accepted Answer · 2016-10-26 15:00:16Z

0

I think max and min parameter are swapped

This

function List(max,min,numLists,numItems){

should be

function List(min,max,numLists,numItems){

answered Oct 26, 2016 at 15:00

Alex González

314 bronze badges

Comments

Eren Akkus · Accepted Answer · 2016-10-26 15:04:38Z

0

Just replace this line;

var randomItem = Math.floor(Math.random() * (1+(this.max-this.min)));

with;

var randomItem = Math.floor(Math.random()*(fullArray.length)+1);

answered Oct 26, 2016 at 15:04

Eren Akkus

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