How to increment a value in a JavaScript object?

Question

var map = {};
map[key] = value;

How can I

• assign value 1 if key does not yet exist in the object
• increment the value by 1 if it

Answer 1

You can check if the object doesn't have the specific key and set it or increase existing key value by one:

function assignKey(obj, key) {
  typeof obj[key] === 'undefined' ? obj[key] = 1 : obj[key]++;
}

var map = {};

assignKey(map, 2);
assignKey(map, 2);
assignKey(map, 4);
assignKey(map, 1);
assignKey(map, 2);
assignKey(map, 5);
assignKey(map, 1);
console.log(map);