Javascript: reference variable in an array within same namespace

Question

I have the following namespace,

var app = {
w: 200,
h: 200,
spacing: 5,
dataList:[
    // 1st column
    [1 * this.w, 1 * this.h, 0 * this.w, 0 * this.h, 'bedroom.jpg', 'Bedroom 1'],
    [1 * this.w, 1 * this.h, 0 * this.w, 1 * this.h, 'topFloorLounge.jpg', 'Top floor lounge'],
    [1 * this.w, 1 * this.h, 0 * this.w, 2 * this.h, 'garage.jpg', 'Garage'],
    // 2nd column
    [2 * this.w, 2 * this.h, 1 * this.w, 0 * this.h, 'livingRoom2.jpg', 'Living room 2'],
    [1 * this.w, 1 * this.h, 1 * this.w, 2 * this.h, 'gym.jpg', 'Gym']
]}

but when I console log my dataList, the result for the dataList[0] is: 0: NaN 1: NaN 2: NaN 3: NaN 4: "bedroom.jpg" 5: "Bedroom 1"

obviously, 'this.w' within the array is not referring to w:200 in the same namespace, what have I done wrong? any suggestions is much appreciated.

Thanks

Ingmar de Lange · Accepted Answer · 2016-04-06 10:28:26Z

3

this.w is not yet a property, you need 2 steps:

var app = {
    w: 200,
    h: 200,
    spacing: 5,
    dataList:[]
};

app.dataList.push(
    // 1st column
    [1 * app.w, 1 * app.h, 0 * app.w, 0 * app.h, 'bedroom.jpg', 'Bedroom 1'],
    [1 * app.w, 1 * app.h, 0 * app.w, 1 * app.h, 'topFloorLounge.jpg', 'Top floor lounge'],
    [1 * app.w, 1 * app.h, 0 * app.w, 2 * app.h, 'garage.jpg', 'Garage'],
    // 2nd column
    [2 * app.w, 2 * app.h, 1 * app.w, 0 * app.h, 'livingRoom2.jpg', 'Living room 2'],
    [1 * app.w, 1 * app.h, 1 * app.w, 2 * app.h, 'gym.jpg', 'Gym']
);

answered Apr 6, 2016 at 10:28

Ingmar de Lange

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Comments

Lewis · Accepted Answer · 2016-04-06 10:41:00Z

1

Your code is executed in global context. This means this will refer to window object. If you want this refer to app object, you need to execute the code within its own methods.

var app = {
  w: 200,
  h: 200,
  spacing: 5,
  dataList: function() {
    return [
      // 1st column
      [1 * this.w, 1 * this.h, 0 * this.w, 0 * this.h, 'bedroom.jpg', 'Bedroom 1'],
      [1 * this.w, 1 * this.h, 0 * this.w, 1 * this.h, 'topFloorLounge.jpg', 'Top floor lounge'],
      [1 * this.w, 1 * this.h, 0 * this.w, 2 * this.h, 'garage.jpg', 'Garage'],
      // 2nd column
      [2 * this.w, 2 * this.h, 1 * this.w, 0 * this.h, 'livingRoom2.jpg', 'Living room 2'],
      [1 * this.w, 1 * this.h, 1 * this.w, 2 * this.h, 'gym.jpg', 'Gym']
    ];
  }
};
app.dataList();

answered Apr 6, 2016 at 10:41

Lewis

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1 Comment

ken chan Over a year ago

thank you, your answer suits my need more as its more self contained and is closer to my originally intended.

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