var obj = {
bob : 14
jan : 2
}
If i add to this object, such as obj.bob = "12", is there a way to add this to make bob : 26 instead of replacing it with bob: 12? Thank you.
4 Answers
You could use an ES6 feature, Proxy
The
Proxyobject is used to define custom behavior for fundamental operations (e.g. property lookup, assignment, enumeration, function invocation, etc).
var obj = { bob: 14, jan: 2 },
p = new Proxy(obj, {
set: function(target, prop, value) {
target[prop] = (target[prop] || 0) + value;
}
});
p.bob = 10;
console.log(p.bob); // 24
p.jane = 42;
console.log(p.jane); // 422 Comments
Cerbrus
I should read more carefully, this is exactly what the OP wants xD
lonesomeday
This can be done without proxies using setters and getters.
So, you use this way.
var obj = {
bob : 14,
jan : 2
}
obj.bob += 12;
console.log(obj);
Comments
var obj = {
bob : 14,
jan : 2
}
obj.bob += 12;
console.log(obj.bob)
Comments
The simple, and almost certainly correct, answer is to use the addition assignment += operator, which adds the right operand to the left operand.
obj.bob += 12; //obj.bob is now 26
You may want to have a system where setting a property with the assignment operator = actually adds the value to the property's existing value. This seems confusing and unlikely to be helpful, but it is technically possible using Object.defineProperty:
let _bob = 14;
Object.defineProperty(obj, 'bob', {
set(newValue) {
_bob += Number(newValue);
},
get() {
return _bob;
}
});
obj.bob = 12;
console.log(obj.bob); // logs '26'
I can't believe this is ever likely to be desired behaviour, however.
2 Comments
Nina Scholz
what do you do with a new property?
lonesomeday
@NinaScholz An initial value is specified in the object literal in the question. This mirrors that.
obj.bob += 12obj.bob = obj.bob ? obj.bob + 12 : + 12