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

You should check if the object has an own property with the new_item name first. If it doesn't, add it and set the value to 1. Otherwise, increment the value:

var dict = {};
var new_item = "Bill"

dict[new_item] = dict.hasOwnProperty(new_item)? ++dict[new_item] : 1;

The above is a bit wasteful as if the property exists, it increments it, then assigns the new value to itself. A longer but possibly more efficient alternative is if the property doesn't exist, add it with a value of zero, then increment it:

if (!dict.hasOwnProperty(new_item)) {
  dict[new_item] = 0;
}
++dict[new_item];