Coffee script : using “constructed” string to call a method

Question

I'm trying to call a method on a class instance in Coffee script by using a string , made from a variable number of user's input fields . Let's say we have a "surface" instance , on which we should call a method for drawing a specific figure . Here is the code in CoffeeScript:

  dojo.ready ->    
    dojoConfig = gfxRenderer: "svg,silverlight,vml"
    surface = dojox.gfx.createSurface("dojocan", 500, 400)
    /  The user's input values are stored in an array
    /  and then concatenated to create a string of this pattern:
    /  formula = "createRect({pointX,pointY,height,width})"
    /  Now I should apply the string "formula" as a method call to "surface" instance

    surface."#{formula}".setStroke("red") 

    / ?? as it would be in Ruby , but .... it fails

I have seen all the similar questions , but I cannot find the answer for implementing it in Coffee Script .

Thank you for your time .

Answer 1

So you have a string like this:

"createRect(pointX,pointY,height,width)"

and you want to call that createRect as a method on surface, right? You're making your life harder and uglier than it needs to be by massing it all together into a single string; instead, you should create two separate variables: a string to hold the method name and an array to hold the arguments:

method = 'createRect'
args   = [ 0, 11, 23, 42 ] # the values for pointX, pointY, height, width

Then you can use Function.apply:

surface[method].apply(surface, args)

If you need to store the method name and arguments in a database somewhere (or transport them over the network), then use JSON.stringify to produce a structured string:

serialized = JSON.stringify(
    method: 'createRect'
    args:   [0, 11, 23, 42]
)
# serialized = '{"method":"createRect","args":[0,11,23,42]}'

and then JSON.parse to unpack the string:

m = JSON.parse(serialized)
surface[m.method].apply(surface, m.args)

Don't throw away the structure you already have, maintain that structure and take advantage of it so that you don't have to waste a bunch of time and effort solving parsing tasks that have already been solved.

Answer 2

Try

surface[formula].setStroke("red") 

Answer 3

I am so happy today! I've learned how to construct strings that calls methods on an class instance . It seems so simple (after mr. MU IS TOO SHORT showed me ):

method = "stringMethodToCall"  # selected by user's input  
arguments = [arrayOfValues] # must be array or array-like object
surface = dojox.gfx.createSurface("dojocan", 500, 400) 

And now :

surface[method].apply(surface,arguments)

Just like mr. CODEMONKEY said , the surface[method] is accessing the object by key .

Thank you once again .