Coffeescript / Javascript - why object attribute is undefined?

Question

I have this function that I'm using it in a Rails 3.1 project:

setPosition: (object) ->
    console.log object
    console.log object.width
    object["position"] = [500, 50] 
    this

The console.log object gives

Object
    height: 600
    position: Array[2]
    title: "Banner for Creative"
    width: 160
    __proto__: Object

but console.log object.width is undefined. Why ?

Please don't name your variables object, use a more descriptive name that avoids ambiguity with native objects. — jaime
– jaime, Commented Dec 1, 2011 at 2:39
Could you add results for console.log (x for x of object) and console.log 'width' of object? It may be that there's a subtle string issue, such as the key name having a null character at the end. See my answer on another question today: stackoverflow.com/a/8344503/66226 — Trevor Burnham
– Trevor Burnham, Commented Dec 1, 2011 at 16:41

Community · Accepted Answer · 2017-05-23 10:08:15Z

3

I answered a similar question just a couple of days ago: https://stackoverflow.com/a/8299394/66226

Basically, console.log has some asynchronous behaviors (in some environments). So when you pass in a reference to an object, that object is stringified later—whereas object.width is undefined right now.

If you do

console.log object.toString()

then you should get more consistent results (though less pretty ones).

Edit: Or better yet,

console.log JSON.stringify(object)

See comments below.

edited May 23, 2017 at 10:08

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answered Dec 1, 2011 at 3:09

Trevor Burnham

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10 Comments

Adam Rackis Over a year ago

+1 - I assumed he was getting an error. I never imagined console.log would have issues like this

Aldo Over a year ago

Adam, I'm not getting an error, just 'undefined'. But if I try to access width or height directly ( object.height for instance ) same behavior.

Aldo Over a year ago

console.log object.toString() gives [object Object]

Trevor Burnham Over a year ago

@Aldo Ah, sorry; try JSON.stringify(object) instead of object.toString().

Trevor Burnham Over a year ago

@Aldo Ah, I misread your post about what JSON.stringify shows—it is an async problem! My answer, as posted above, is correct. Everything but console.log object is showing the true state of the object at the time of the console.log; console.log object is storing a reference to the object, then displaying it later, after the object's fields have been populated. Use JSON.stringify when you want to avoid confusion! Make sense?

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