js how to implement map[index]++ concisely

问题

With Array, I can use array[index]++

But with Map, I only know map.set(index,map.get(index)+1)

I think it looks bad, and if index is a long name function, I have to split it into two lines.

Is there a more concise way to implement map[index]++

回答1:

I could only suggest a helper function, like

function update(map, key, fn) {
    return map.set(key, fn(map.get(key), key));
}

update(table, index, i=>i+1);

There is no syntactic sugar for assignments, and therefore no shorthand assignments either.

---

If your keys are strings, you could employ a Proxy with suitable traps to disguise the update as a property access.

const mapMethods = {
    has: Function.prototype.call.bind(Map.prototype.has),
    get: Function.prototype.call.bind(Map.prototype.get),
    set: Function.prototype.call.bind(Map.prototype.set),
};
function asObject(map) {
    return new Proxy(map, mapMethods);
}

asObject(table)[index]++;

_{Disclaimer: Please don't do that. It's scary.}

来源：https://stackoverflow.com/questions/48897716/js-how-to-implement-mapindex-concisely