如果来自对象的相同键添加值

Question

var obj = {
bob : 14
jan : 2
}

如果我添加到这个对象，比如obj.bob = "12"，有没有办法添加它来制作 bob : 26 而不是用 bob: 12 替换它？谢谢你。

Answer 1

所以，你用这种方式。

var obj = {
bob : 14,
jan : 2
}

obj.bob += 12;

console.log(obj);

Answer 2

var obj = {
  bob : 14,
  jan : 2
}

obj.bob += 12;
console.log(obj.bob)

Answer 3

您可以使用 ES6 功能，Proxy

The Proxy object 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); // 42

Answer 4

简单且几乎肯定正确的答案是使用 addition assignment += operator，它将右操作数添加到左操作数。

obj.bob += 12; //obj.bob is now 26

您可能想要一个系统，其中设置属性与 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'

然而，我不敢相信这可能是理想的行为。

如果来自对象的相同键添加值

Add Value if Same Key from Object

javascript

key

object

key-value