Check if a variable exists - Memory ?

[espruino-discuss]

Posted at 2014-04-12 by Sacha

Hi Espruinos,

I just searching a proper way to detect if a variable is defined/exists without loosing memory. Yes it's all about memory....

I tried it in two ways:

 if(variable !==undefined)

and

if(typeof variable !=='undefined')

Here is the memory loosing code:

test={};

console.log(process.memory());
for(i=0;i<1000;i++) {
  if(test['hello'+i]!==undefined)
  {
    console.log('hello'+i+' is defined');
  }
}
console.log(process.memory());

Output:

{"free":1780,"usage":20,"total":1800,"history":5,"stackEndAddress":536909512,"flash_start":134217728,"flash_binary_end":134432224,"flash_code_start":134443008,"flash_length":262144}
{"free":778,"usage":1022,"total":1800,"history":18,"stackEndAddress":536909512,"flash_start":134217728,"flash_binary_end":134432224,"flash_code_start":134443008,"flash_length":262144}

Each test if the variable exists creates the variable as undefined and uses memory.
You will see it when you output the array like this:

console.log(test);

Output:

{"hello0":undefined,"hello1":undefined,"hello2":undefined,"hello3"...........

Many thanks for your help

Sacha

[espruino-discuss]

Posted at 2014-04-12 by DrAzzy

This is nasty!

Does 'delete varname' clean up after it?

[espruino-discuss]

Posted at 2014-04-13 by Sacha

Hi DrAzzy,

Yes as any other variable it could be deleted. It gives the mem back.

Sacha

[espruino-discuss]

Posted at 2014-04-14 by graf

I believe it's this one espruino/Espruino#63

Just an idea I didn't test, but how about

if (Object.keys(test).indexOf("bar") !== -1) {...}

Would that make sense?

[espruino-discuss]

Posted at 2014-04-14 by Sacha

Yes, it looks like. Thanks. Will try it.

Sacha

[gfwilliams]

Posted at 2014-04-14 by @gfwilliams

Or you can do if ("bar" in test) ... which is a bit faster/easier.

At the moment this is a frustrating issue - but it's surprising how rarely it's actually a problem if your code is working as expected.