Is there a better way to check the value is not empty or null than this

Question

I just took a project from another developer, and there are many such statements in the code:

if( value != null || value != "" || value != undefined ) { doSomeThing(); } 

Which, while good, becomes a bit messy when used throughout. Is there a better, more accurate way to write this? I thought about it

 if( value.length > 0 || value != undefined ) { doSomeThing(); } 

What do you all think?

thanks

Stephen

Answer 1

This is almost true, but with if( value.length > 0 || value != undefined ) when null value.length will value.length TypeError runtime error: Error # 1009 when you try to access a property with null value.

so you need to check before that the value is not equal to zero, for example:

if (value!=null&&value.length>0) {doSomeThing();}

or another form shorter:

 if ((value||"").length>0) {doSomeThing();} 

One note: If the value type is not * , it cannot be undefined, it will be null .

 var str:String=undefined; trace(str==null); // will output true 

Answer 2

I like to write statements more positively. Programmer statements verify that something is not empty, but it means; if it exists:

In the case of arrays or strings, I use this:

  if ( value && value.length > 0 ) doSomething(); 

But in the case of objects or DisplayObjects, I use this to check if it exists.

  if ( mc ) doSomething(); 

In most cases, this is enough.

Answer 3

Here are some timeline codes for you.

 import flash.display.MovieClip; import flash.display.Sprite; var object : Object; var array : Array; var number : Number; var integer : int; var uinteger : uint; var string : String; var xml : XML; var regexp : RegExp; var movieClip : MovieClip; var array2 : Array = []; var object2 : Object = {}; trace( "uninstantiated Object =", object, "Boolean cast =", Boolean( object ) ); trace( "uninstantiated Array =", array, "Boolean cast =", Boolean( array ) ); trace( "uninstantiated Number =", number, "Boolean cast =", Boolean( number ) ); trace( "uninstantiated int =", integer, "Boolean cast =", Boolean( integer ) ); trace( "uninstantiated uint =", uinteger, "Boolean cast =", Boolean( uinteger ) ); trace( "uninstantiated String =", string, "Boolean cast =", Boolean( string ) ); trace( "empty String =", "", "Boolean cast =", Boolean( "" ) ); trace( "uninstantiated XML =", xml, "Boolean cast =", Boolean( xml ) ); trace( "uninstantiated RegExp =", regexp, "Boolean cast =", Boolean( regexp ) ); trace( "uninstantiated MoveClip =", movieClip, "Boolean cast =", Boolean( movieClip ) ); trace( "instantiated Array with length 0 XML =", array2, "Boolean cast =", Boolean( array2 ) ); trace( "instantiated Object with no properties =", object2, "Boolean cast =", Boolean( object2 ) ); trace( "uninstantiated index of instantiated array =", array2[4], "Boolean cast =", Boolean( array2[4] ) ); trace( "uninstantiated property of instantiated object =", object2[ "color" ], "Boolean cast =", Boolean( object2[ "color" ] ) ); try { //will throw an error trace( "uninstantiated property of uninstatinated class =", movieClip.x, "Boolean cast =", Boolean( movieClip.x ) ); } catch ( e : Error ) {} /* output: uninstantiated Object = null Boolean cast = false uninstantiated Array = null Boolean cast = false uninstantiated Number = NaN Boolean cast = false uninstantiated int = 0 Boolean cast = false uninstantiated uint = 0 Boolean cast = false uninstantiated String = null Boolean cast = false empty String = Boolean cast = false uninstantiated XML = null Boolean cast = false uninstantiated RegExp = null Boolean cast = false uninstantiated MoveClip = null Boolean cast = false instantiated Array with length 0 XML = Boolean cast = true instantiated Object with no properties = [object Object] Boolean cast = true uninstantiated index of instantiated array = undefined Boolean cast = false uninstantiated property of instantiated object = undefined Boolean cast = false As you can see, in general, you can just test for instantiation by using if ( variableName ) ... But this will fail if you want to think of instantiated-but-empty Arrays and Objects as false. Note that it will also fail, generating an error, if you check for properies of uninitialized classes, eg var sprite : Sprite; if ( sprite.x ) trace( "found x" ); //error, because sprite = null and null doesn't have an x property. You can write a more liberal test like this: */ function exists( value : * ) : Boolean { var result : Boolean = true; if ( ! value ) return false; if ( value is Array && ! value.length ) return false; if ( value.constructor.toString() == "[class Object]" ) { result = false; for each ( var prop in value ) { result = true; break; } } return result; } //tests trace( "exists( object ) =", exists( object ) ); trace( "exists( array ) =", exists( array ) ); trace( "exists( number ) =", exists( number ) ); trace( "exists( integer ) =", exists( integer ) ); trace( "exists( uinteger ) =", exists( uinteger ) ); trace( "exists( string ) =", exists( string ) ); trace( "exists( '' ) =", exists( "" ) ); trace( "exists( xml ) =", exists( xml ) ); trace( "exists( regexp ) =", exists( regexp ) ); trace( "exists( movieClip ) =", exists( movieClip ) ); trace( "exists( array2 ) =", exists( array2 ) ); trace( "exists( object2 ) =", exists( object2 ) ); trace( "exists( array2[4] ) =", exists( array2[4] ) ); trace( "exists( object2[ 'color' ] ) =", exists( object2[ "color" ] ) ); var sprite : Sprite = new Sprite(); trace( "INSTANTIATED: exists( sprite ) = ", exists( sprite ) ); var object3 : Object = { color : 0xFFFFFF }; trace( "INSTANTIATED OBJECT WITH PROPERTY: exists( object3 ) =", exists( object3 ) ); var array3 : Object = [ 1 ]; trace( "INSTANTIATED ARRAY WITH LENGTH: exists( array3 ) =", exists( array3 ) ); /* output: exists( object ) = false exists( array ) = false exists( number ) = false exists( integer ) = false exists( uinteger ) = false exists( string ) = false exists( '' ) = false exists( xml ) = false exists( regexp ) = false exists( movieClip ) = false exists( array2 ) = false exists( object2 ) = false exists( array2[4] ) = false exists( object2[ 'color' ] ) = false INSTANTIATED: exists( sprite ) = true INSTANTIATED OBJECT WITH PROPERTY: exists( object3 ) = true INSTANTIATED ARRAY WITH LENGTH: exists( array3 ) = true One more note: be careful with ints and uints. They are always initialized. Whereas other variables point to null, undefined or NaN until you give them values, ints and uints are automatically intialized to zero. There is not way to have an int that doesn't point to a value: var num : Number; var i : int; trace( num ); // NaN trace( i ); //0 In general, that okay, because 0 == false: var i : int; if ( i ) trace( "false" ); //false But I've mixed myself up before with code like this: var color : int = getColorValueFromXML(); if ( color ) drawCircleWithColor( color ); In the above code, I only want to draw a circle if color is initialized. However, color will ALWAYS bee initialized, to zero if not to anything else. But what if getColorValueFromXML() returns 0x00000. We think of that as the color black. But I see a black circle, because 0x000000 is also the same as 0. And, in a conditional, 0 parses as false: if ( 0x000000 ) drawCircleWithColor(); //drawCircleWithColor won't run! */