How to increment an object property value if it exists, else set the initial value?

Question

How might I add check to see if a key already exists, and if does, increment the value, and if it doesn\'t exist, then set the initial value?

Something like this pseudo-

Answer 1

Your pseudo-code is almost identical to the actual code:

if (key in object) {
    object[key]++;
} else {
    object[key] = 1;
}

Although I usually write:

if (!(key in object)) {
    object[key] = 0;
}

object[key]++;