How to use "trace()" to see the data structure of JsVar

[espruino-discuss3]

Posted at 2015-06-22 by Long

I want to know the detail of the data structure of 'JsVar'. In the Terminal, firstly, I type

digitalWrite([A5,A6],0b11);
```.
Then I type 

trace()

, but it dump out the text that troubles me. (the dumped text is in the image file). Could someone  explain it for me ?

 
 

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[espruino-discuss3]

Posted at 2015-06-22 by @gfwilliams

Hi,

You can basically ignore the first block (">") as those are internal datastructures for the interpreter. You also won't see anything in response to your call digitalWrite([A5,A6],0b11), because the function is executed but nothing is stored.

Perhaps it's more useful to pass what you're interested in as an argument to trace() - for instance:

>trace([A5,A6])
#149[r0,l1] Array(2) [
  #146[r1,l2] Name Integer 0    #82[r1,l1] Pin 5
  #145[r1,l2] Name Integer 1    #147[r1,l1] Pin 6
]

Or:

>trace(function(a) { console.log("Hello World"+a); });
#112[r0,l1] Function {
  #110[r1,l2] Name Param "a"     undefined
  #123[r1,l2] Name String [1 blocks] "ÿcod"    #111[r1,l1] String [4 blocks] "{ console.log(\"Hello World\"+a); }"
}

There's a bit of information on what this actually means on the Internals page - you might also get some ideas from the page on performance too

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Posted at 2015-06-22 by Long

yeah, thank you.
but would you explain what the texts like "#149[r0,l1]" or "ycod" mean.
Are #110[r1,l2] Name Param "a" and #123[r1,l2] Name String [1 blocks] "ÿcod" the two children of this funtion?

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Posted at 2015-06-22 by @gfwilliams

but would you explain what the texts like "#149[r0,l1]" or "ycod" mean.

• Reference number 149 (this is the JsVar at jsVars[149+1])
• 0 references (no other variable links to it)
• 1 lock (some bit of code has a pointer to this variable - probably 'trace' itself)

ycod is the special name of the variable that contains the function's code. It's JSPARSE_FUNCTION_CODE_NAME

Are #110[r1,l2] Name Param "a" and #123[r1,l2] Name String [1 blocks] "ÿcod" the two children of this funtion?

Yes, that's right.