Howto isset Method? without initilize instance

[maborak]

loading..............



var a =function()
{
this.b=function(){};
}

//howto isset this.b ?
WITHOUT

var g= new a(); // without instance

var isset = g.b || false;




connection closed.

 

[RobG]

loading..............

var a =function()
{
this.b=function(){};

}

//howto isset this.b ?
WITHOUT

var g= new a(); // without instance

var isset = g.b || false;

I don't really get what you are on about, my guess is that you want to
test for g.b but don't know if g is defined in the first place. Maybe
you want:

var isset = !!(g && g.b);

 

[-Lost]

I don't really get what you are on about, my guess is that you want to
test for g.b but don't know if g is defined in the first place. Maybe
you want:

var isset = !!(g && g.b);

Is that a magic trick?

 

[RobG]

Is that a magic trick?

No, it's using the && (AND) operator as what Douglas Crockford calls a
"guard" operator.

The expressions inside the brackets are evaluated from left to right
until either one of them resolves to false (or its equivalent: null,
undefined or numeric zero) or the last expression is reached.

The value of the last expression evaluated is returned, whereupon !!
converts it to boolean false (if it is one of the previously mentioned
values) or true (for any other value).

Note that strings '0' (zero), 'false', 'null', etc. resolve to true.

 

[-Lost]

No, it's using the && (AND) operator as what Douglas Crockford calls a
"guard" operator.

The expressions inside the brackets are evaluated from left to right
until either one of them resolves to false (or its equivalent: null,
undefined or numeric zero) or the last expression is reached.

The value of the last expression evaluated is returned, whereupon !!
converts it to boolean false (if it is one of the previously mentioned
values) or true (for any other value).

Note that strings '0' (zero), 'false', 'null', etc. resolve to true.

Ah yes, in the survey. I had forgotten about that. To be honest I did
not quite understand it until your explanation. (Granted it is still
remarkably fuzzy.)

Thanks.