Check if a variable exists - Memory ?

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

This is nasty!

Does 'delete varname' clean up after it?

Hi DrAzzy,

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

Sacha

I believe it's this one https://github.com/espruino/Espruino/issues/63

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

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

Would that make sense?

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

Sacha

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.