Due to object in javascript is associative map (HashMap in other programming languages) does next code
for (var prop in object) {
if (prop === someConcreteProperty) {
// some decision
break;
}
}
slower anyhow then dummy property lookup like
if (typeof object.someConcreteProperty != 'undefined') {
// some decision
}
Edits:
I'm thinking about performance in code like:
for ( var prop in obj)
if (obj[prop] === someAnonymousMethod) {
// I need that property name for my need
return obj.prop();
}
will it be twice property lookup time like
obj.prop()
or more?
Thanks.
Best Answer
This can be tested empirically:
Method 1 takes MUCH longer than Method 2. This is hardly surprising since all of the computing necessary to execute Method 2 is included in Method 1 plus MUCH more.