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I've just started down my path of really learning JavaScript. My first stop was "JavaScript: The Good Parts", and the author there really advocates using closur

by city41 16y ago

I've just started down my path of really learning JavaScript. My first stop was "JavaScript: The Good Parts", and the author there really advocates using closures to define objects and enable encapsulation. It seems in practice this approach isn't used often (such as Backbone here), why is that?

oscilloscope 16y ago
Take a look at the source-- Backbone itself is written in the module pattern. Underscore and Backbone will both teach you a lot. This chapter from Eloquent Javascript will also help motivate the rationale behind Underscore: http://eloquentjavascript.net/chapter6.html http://eloquentjavascript.net/chapter6.html
jimmydo 16y ago
The mostly likely reason is probably familiarity. Most languages use the 'new' operator to create new objects, so it seems natural to follow the same pattern when creating a JS API that will likely be consumed by people who come from other languages. The main advantage of Douglas Crockford's power constructor pattern is that it allows truly private variables or functions. I used to be adamant that this was the right way to go (and I still appreciate the pattern), but then I found that just following the convention of prefixing private members with an underscore worked fine--most people understand that it means "private". My code also started to look a little neater. All of my instance members are actually tied to the 'this' context object, rather being spread between nested functions or local variables declared within the constructors, and public/privileged methods declared on the new object itself.
munificent 16y ago
Performance. If you have n objects with m methods, that creates n * m function objects. With "normal" prototypal inheritance where those methods are on the prototype, it only requires n objects + m functions.
- jashkenas 16y ago
  As always, munificent is right on the money. The "closure pattern" is one of the most serious JavaScript anti-patterns -- it doesn't make much of a difference in tiny scripts, but for any decent-size JavaScript application, it can hurt performance terribly, especially regarding memory use. For example, benchmarking the creation of 1 million objects, each with 10 member functions, in both the prototypal style and the closure style (in Chrome): 1 million prototypal objects: Brief pause, 32.4 MB 1 million closure objects: Minutes wait, 368.1 MB If you're doing object-oriented code in JS, please use the "prototype" property, like the language is designed to do. For more info, here's Brendan Eich on the subject: http://www.aminutewithbrendan.com/pages/20110216 http://www.aminutewithbrendan.com/pages/20110216
  - nxn 16y ago
    I don't even know if this can be considered the "closure" pattern anymore, but I wanted to try to get method sharing among the objects by doing something like this: https://gist.github.com/877259 https://gist.github.com/877259 The hope was that since the functions were created and bound within the function literal, the "create" method could simply assign references to the existing functions instead of creating a new function each time (ie, avoid what munificent mentioned). Funny thing is, even though the last line indicates that the first and last objects' "ten" method is actually shared between them, I'm still getting about 370 MB of memory usage after creating 1 million objects. I am under assumption that the cause of this memory increase is the fact that each one of the million objects has its own local references to each of the 10 functions. When I put the 10 functions inside of the "create" method, memory usage goes up again to roughly 750 MB.
  - jimmydo 16y ago
    That was a really interesting talk--thanks for the link! Something that initially confused me was that Eich's use of the term "prototypal" (a pattern for implementing class-based inheritance) was different from Douglas Crockford's use of it (an alternative to class-based inheritance - http://javascript.crockford.com/prototypal.html http://javascript.crockford.com/prototypal.html). In case anyone else finds this useful, here's how I sorted it out: - "class-based" & "prototype-based" inheritance (Crockford refers to them as "classical" & "prototypal" inheritance). Different styles of instantiating objects. - "closure pattern" & "prototypal pattern" (aka "prototypal inheritance" in this context). Different techniques for implementing class-based inheritance.

by city41 16y ago

oscilloscope 16y ago

Take a look at the source-- Backbone itself is written in the module pattern. Underscore and Backbone will both teach you a lot. This chapter from Eloquent Javascript will also help motivate the rationale behind Underscore: http://eloquentjavascript.net/chapter6.html http://eloquentjavascript.net/chapter6.html

jimmydo 16y ago

The mostly likely reason is probably familiarity. Most languages use the 'new' operator to create new objects, so it seems natural to follow the same pattern when creating a JS API that will likely be consumed by people who come from other languages. The main advantage of Douglas Crockford's power constructor pattern is that it allows truly private variables or functions. I used to be adamant that this was the right way to go (and I still appreciate the pattern), but then I found that just following the convention of prefixing private members with an underscore worked fine--most people understand that it means "private". My code also started to look a little neater. All of my instance members are actually tied to the 'this' context object, rather being spread between nested functions or local variables declared within the constructors, and public/privileged methods declared on the new object itself.

munificent 16y ago

Performance. If you have n objects with m methods, that creates n * m function objects. With "normal" prototypal inheritance where those methods are on the prototype, it only requires n objects + m functions.

jashkenas 16y ago
As always, munificent is right on the money. The "closure pattern" is one of the most serious JavaScript anti-patterns -- it doesn't make much of a difference in tiny scripts, but for any decent-size JavaScript application, it can hurt performance terribly, especially regarding memory use. For example, benchmarking the creation of 1 million objects, each with 10 member functions, in both the prototypal style and the closure style (in Chrome): 1 million prototypal objects: Brief pause, 32.4 MB 1 million closure objects: Minutes wait, 368.1 MB If you're doing object-oriented code in JS, please use the "prototype" property, like the language is designed to do. For more info, here's Brendan Eich on the subject: http://www.aminutewithbrendan.com/pages/20110216 http://www.aminutewithbrendan.com/pages/20110216
- nxn 16y ago
  I don't even know if this can be considered the "closure" pattern anymore, but I wanted to try to get method sharing among the objects by doing something like this: https://gist.github.com/877259 https://gist.github.com/877259 The hope was that since the functions were created and bound within the function literal, the "create" method could simply assign references to the existing functions instead of creating a new function each time (ie, avoid what munificent mentioned). Funny thing is, even though the last line indicates that the first and last objects' "ten" method is actually shared between them, I'm still getting about 370 MB of memory usage after creating 1 million objects. I am under assumption that the cause of this memory increase is the fact that each one of the million objects has its own local references to each of the 10 functions. When I put the 10 functions inside of the "create" method, memory usage goes up again to roughly 750 MB.
- jimmydo 16y ago
  That was a really interesting talk--thanks for the link! Something that initially confused me was that Eich's use of the term "prototypal" (a pattern for implementing class-based inheritance) was different from Douglas Crockford's use of it (an alternative to class-based inheritance - http://javascript.crockford.com/prototypal.html http://javascript.crockford.com/prototypal.html). In case anyone else finds this useful, here's how I sorted it out: - "class-based" & "prototype-based" inheritance (Crockford refers to them as "classical" & "prototypal" inheritance). Different styles of instantiating objects. - "closure pattern" & "prototypal pattern" (aka "prototypal inheritance" in this context). Different techniques for implementing class-based inheritance.