node.js用未知键对数字desc排序对象？

Question

how can i sort this object by value DESC when the keys are unknown?

var themen = {"Eisenbahn":2,"Technik":2,"Mathematik":3,"Automobil":4,"Physik":1,"Computer":2,"Ökonomie":1}

Edit:

The following codes generates a Map that suits my requirement, unfortunately it cannot be converted to json via JSON.stringify() and just returns {}

themen = new Map(Object.keys(themen).map(function(v) {
    return [v, themen[v]]
}).sort(function(p,t) {
    return t[1] - p[1];
}));

any ideas how to make it to json and keep the order?

Answer 1

Objects have no order, the order in which you add the properties to the object is the order in which they appear.

So can build an object based on the first and adding the properties in the order in which you prefer.

This works:

var orderThemen = function (themen) {
  var themens = Object.keys(themen)
  var order = {}
  var output = {}

  themens.forEach(function (key) {
    var auxThemen = themen[key]
    if (!order[auxThemen]) order[auxThemen] = []    
    order[auxThemen].push(key)
  })    

  Object.keys(order).forEach(function (key) {
    var level = order[key]
    level.forEach(function (themen) {
      output[themen] = key
    })
  })

  return output
}

Answer 2

So close ...

Change your map line to

themen = Object.keys(themen).map(function(v) {
    return [v, themen[v]]
}).sort(function(p,t) {
    return t[1] - p[1];
});

new Map() creates a Map object which is something else.

Edit:

Unless you want the object again ...

var result = {}
Object.keys(themen).map(function(v) {
    return [v, themen[v]]
}).sort(function(p,t) {
    return t[1] - p[1];
}).forEach(function(v){
    result[v[0]] = v[1];
});
console.log(result); // => sorted object