using functions inside javascript constructors

Question

I need to write a constructor for an object that gives a random value to the object's color property. This is what I wrote

var Ghost = function() {
  // your code goes here
  var num = Math.floor(Math.rand()*4);
  if(num === 0){
    this.color = "white";
  }
  else if(num === 1){
    this.color = "yellow";
  }
  else if(num === 2){
    this.color = "purple";
  }
  else if(num === 3){
    this.color = "red";
  }
};

I get an error message from the test suite on code wars

TypeError: Object #<Object> has no method 'rand'
   at new Ghost
        at Test.describe

Am I not allowed to use functions inside a constructor or is there something about the test suite I don't understand?

Do you mean Math.random()? There's no Math.rand() function. — ntalbs
– ntalbs, Commented Dec 6, 2014 at 4:12

Fengyang Wang · Accepted Answer · 2014-12-06 04:13:28Z

3

The name of the function is Math.random, not Math.rand.

To interpret the error message:

TypeError: Object #<Object> has no method 'rand'

First try to find the object with the "rand" method you are trying to call. In this case, it is Math. Then verify that the object in question indeed has the method.

On an unrelated note, your selection code can be simplified to:

var COLOURS = ['white', 'yellow', 'purple', 'red'];
this.color = COLOURS[Math.floor(Math.random() * 4)];

answered Dec 6, 2014 at 4:13

Fengyang Wang

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1 Comment

jfriend00 Over a year ago

Even better to change the 4 to COLOURS.length.

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