Cannot access the variable in the object

Question

I want to access the variable in the object, something like below:

var menuSetup = { m : [100,200], height: m[0], // m is not defined } var menuSetup = { m : [100,200], height: this.m[0], // I tried this, still failed }

So can I access the variable in the object?

You could define a variable outside of the object and use that in both places. jsfiddle.net/5taBt — Patrick Q
– Patrick Q, Commented Jul 17, 2014 at 18:49
Why would you want to do this? It would cause cluttering. What you really want here is an object with a method height() that returned the value you want. — Casey Falk
– Casey Falk, Commented Jul 17, 2014 at 18:52

soktinpk · Accepted Answer · 2014-07-17 18:54:36Z

Unfortunately, you can't do that. This is because the properties of menuSetup haven't been defined yet. For example,

var menuSetup = { m: [100, 200], height: menuSetup.m[0] };

will through (in chrome) TypeError: Cannot read property 'm' of undefined because menuSetup is just undefined (because it was hoisted by the var declaration)

The only two ways I can think of is to

a) Save m as a variable before. For example:

var m = [100, 200]; var menuSetup = { m: m, height: m[0] }

b) Use a method instead of a variable and execute it.

var menuSetup = { m: [100, 200], height: function() { return this.m[0]; } }

Then, when you get menuSetup.height, you would actually do menuSetup.height().

Comfortably Numb · Accepted Answer · 2014-07-17 18:54:48Z

0

You can try this:

var MenuSetup = function() { this.m = [100,200]; this.height = this.m[0]; } var menuSetup = new MenuSetup(); console.log(MenuSetup.height);

answered Jul 17, 2014 at 18:54

Comfortably Numb

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3 Comments

mc01 Over a year ago

I always get beat out by about 15 seconds :P

soktinpk Over a year ago

Shouldn't the constructor start with a capital letter and the instance start with the lower i.e. var menuSetup = new MenuSetup()?

Comfortably Numb Over a year ago

@soktinpk good point, I was keeping OP casing but you're right this is different and merit changing.

Community · Accepted Answer · 2017-05-23 12:21:25Z

Not the way you're doing it. In JavaScript you cannot reference another property while creating the same object, because the object doesn't yet exist until after the closing } at the end.

You could use a constructor function instead though, as explained in answers to this similar question.

function MenuSetup() { this.m = [100, 200]; this.height = this.m[0]; } var menu = new MenuSetup(); console.log(menu.height) //100

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