You can use the in
operator:
if (direction in room.exits) {
// go that way
} else {
console.log("you can't go that way!");
}
Pregunta
In the text adventure I am making, my object literals for the rooms look like this:
room : {
// some info,
exits : {
north : -1,
east : "house",
south : "forest",
west : -1
}
}
and in my function to move around it says:
if (room["exits"][direction] !== -1) {// go that way}
else {print "you can't go that way!"}
now I want to save space by just testing if the key for the relevant direction exits in the object. so the literals will go:
room : {
// some info,
exits : {
east : "house",
south : "forest"
}
}
... what should my if
statement look like? what is the 'proper' way to ascertain if a given key-name exits in the object?
Solución
You can use the in
operator:
if (direction in room.exits) {
// go that way
} else {
console.log("you can't go that way!");
}
Otros consejos
If there's absolutely no chance that it'll be null, a blank string, zero, or any other 'falsey' JS value you can just do
if(room.exits[direction]) { // go that way }
else {print "you can't go that way!"}
I also did a speed test against the 'in' operator that p.s.w.g posted as an answer because it never really occurred to me to use it. I found some interesting results that you should consider if you're running this in any kind of loop at any point.
http://jsperf.com/test-in-operator-vs-if
It seems that the "in" operator is SIGNIFICANTLY slower on IE and Chrome, but on Firefox it's almost twice as fast.
you should do:
if (room.exits.south) {// go that way}
else {print "you can't go that way!"}
that's it.
When "south" is undefined (or when it is zero or empty string or literal false), the predicate evaluates to false.