Absence of boolean variabl vs FALSE value of variable

Richard Haseltine

I've been writing a script to read certain values from a .dsf morph asset file. One of the things I want to check is whether the morph is hidden. Unfortunately sometimes the visible variable is missing from the asset file, and DS treats that as being visible = true, but in scripting using

if ( ! ourObject.modifier_library[ n ].channel.visible )

is true both if the variable is present and set to false (morph hidden) and if the variable is absent (morph visible). I've got around this by sending ourObject.modifier_library[ n ].channel to a custom checker function:

function morphVis ( object ) {
 // find if object contaisn a property "Visible"
 // if it does, return its value, if not return true
 // as lack of the property seems to be treated that way
 
 var str;
 for ( var n in object ) {
  str = "" + n;
  if ( str == "visible" ) {
   return n.value;
  }
 }
 return true;
}

and it occurs to me I could also use JSON.stringify( ourObject.modifier_library[ n ].channel ).find( "visible" ) as a test, but both seem somewhat Heath-Robinsonish. Is there a better way to distinguish between the absence of a boolean variable in a data structure and its presence with a value of false?

millighost

Richard Haseltine said:

I've been writing a script to read certain values from a .dsf morph asset file. One of the things I want to check is whether the morph is hidden. Unfortunately sometimes the visible variable is missing from the asset file, and DS treats that as being visible = true, but in scripting using

if ( ! ourObject.modifier_library[ n ].channel.visible )

is true both if the variable is present and set to false (morph hidden) and if the variable is absent (morph visible). I've got around this by sending ourObject.modifier_library[ n ].channel to a custom checker function:

function morphVis ( object ) {
 // find if object contaisn a property "Visible"
 // if it does, return its value, if not return true
 // as lack of the property seems to be treated that way
 
 var str;
 for ( var n in object ) {
  str = "" + n;
  if ( str == "visible" ) {
   return n.value;
  }
 }
 return true;
}

and it occurs to me I could also use JSON.stringify( ourObject.modifier_library[ n ].channel ).find( "visible" ) as a test, but both seem somewhat Heath-Robinsonish. Is there a better way to distinguish between the absence of a boolean variable in a data structure and its presence with a value of false?

something like this should work:

var channel = ourObject.modifier_library[ n ].channel;
/*
 * set is_visible to true if visible is missing or present and true.
 */
var is_visible = !('visible' in channel) || channel.visible;

Richard Haseltine

Ah, so I don't have to convert to string with the right approach. I'd tried n (as inb the loop ) == "visible" but that didn't work (not surprisingly), hence assigning it with the addition of "" to force it to act as a string. Thanks.

rbtwhiz

You can use Object.hasOwnProperty() to check whether an Object instance has a property. Notice that the majority of the example below is for testing/debugging.

/*********************************************************************/
// Number : This function returns 1 if the property is true,
// 0 if the property is false or -1 if the property is missing
function getBoolPropertyValue( oObject, sName ){
 if( oObject.hasOwnProperty( sName ) ){
  return Number( oObject[ sName ] );
 }
 return -1;
};

/*********************************************************************/
// Create our test object
var oTestObject = { "visible" : false };

// Debug
var sName = "visible";
var nValue = getBoolPropertyValue( oTestObject, sName );
var sStatus;
switch( nValue ){
 default:
 case -1: sStatus = "missing"; break;
 case 0: sStatus = "false"; break;
 case 1: sStatus = "true"; break;
}
print( String("The %1 property is %2.").arg( sName ).arg( sStatus ) );

The function above answers the question in the subject... the absence of a Boolean property vs. the value of a Boolean property.

-Rob

Richard Haseltine

Thanks, that looks as if it should be simple to generalise too.