Javascript-在每个循环中制作对象并增加数组中的计数

Question

I am trying to create an object from a forEach loop in javascript and in this simple object, I am trying to add up all of the count s for each item in the array.

Currently, I'm using firebase in an ionic (angular/typescript) project and I am returning an array of items from firebase. The array looks something like this:

[
    {
        id:'uniqueID',
        specs: {
            count:5,
            forSale:false,
            group:"qPELnTnwGJEtJexgP2qX",
            name:"Foxeer Cam 2",
            type:"camera"
        }
    },
    {
        id:'uniqueID',
        specs: {
            count:4,
            forSale:false,
            group:"qPELnTnwGJEtJexgP2qX",
            name:"Furibee 40a",
            type:"esc"
        }
    },
    {
        id:'uniqueID',
        specs: {
            count:4,
            forSale:false,
            group:"qPELnTnwGJEtJexgP2qX",
            name:"Runcam Cam 1",
            type:"camera"
        }
    },
    {
        id:'uniqueID',
        specs: {
            count:1,
            forSale:false,
            group:"qPELnTnwGJEtJexgP2qX",
            name:"Hobbywing 4 in 1",
            type:"esc"
        }
    }
]

Here's how I'm running through these items ( result being the list of items):

let partArr = [];
let typeObj = {};
result.forEach(part => {

  //Put all parts in a list
  partArr.push({
    'id':part.id,
    'specs':part.data(),
  });

  //Put all types in a list
  typeObj[part.data().type] = {
    'count': 0
  };

});

Now, I need to increment the count, adding each part's count to the last depending on their type. The typeObj should look something like this.

{
    esc: {
        count:5
    },
    camera: {
        count:10
    }
}

I tried adding the count to the count like so:

  typeObj[part.data().type] = {
    'count': typeObj[part.data().type].count + part.data().count
  };

but it does not recognize there being a count when I'm first making the object. (I think).

Any advice?

Answer 1

It would probably be easier to use reduce to generate the object with the counts all at once, and to call .data() only once on each iteration:

 const results = [ { data() { return { specs: { count:5, forSale:false, group:"qPELnTnwGJEtJexgP2qX", name:"Foxeer Cam 2", type:"camera" }}}}, { data() { return { specs: { count:4, forSale:false, group:"qPELnTnwGJEtJexgP2qX", name:"Furibee 40a", type:"esc" }}}}, { data() { return { specs: { count:4, forSale:false, group:"qPELnTnwGJEtJexgP2qX", name:"Runcam Cam 1", type:"camera" }}}}, { data() { return { specs: { count:1, forSale:false, group:"qPELnTnwGJEtJexgP2qX", name:"Hobbywing 4 in 1", type:"esc" }}}} ]; const typeObj = results.reduce((a, item) => { const { count, type } = item.data().specs; if (!a[type]) a[type] = { count: 0 }; a[type].count += count; return a; }, {}); console.log(typeObj); 

Answer 2

You can use Array#reduce to accomplish this since you want to transform an array into a single object:

 const array = [ { id: 'uniqueID', specs: { count: 5, forSale: false, group: "qPELnTnwGJEtJexgP2qX", name: "Foxeer Cam 2", type: "camera" } }, { id: 'uniqueID', specs: { count: 4, forSale: false, group: "qPELnTnwGJEtJexgP2qX", name: "Furibee 40a", type: "esc" } }, { id: 'uniqueID', specs: { count: 4, forSale: false, group: "qPELnTnwGJEtJexgP2qX", name: "Runcam Cam 1", type: "camera" } }, { id: 'uniqueID', specs: { count: 1, forSale: false, group: "qPELnTnwGJEtJexgP2qX", name: "Hobbywing 4 in 1", type: "esc" } } ]; const typeObj = array.reduce((obj, { specs: { count, type } }) => { obj[type] = obj[type] || { count: 0 }; obj[type].count += count; return obj; }, {}); console.log(typeObj); 

What this does is assign obj[type] to either itself or if it doesn't yet exist, a new object { count: 0 } . Then it increments the count property of obj[type] by the specified count in the data.

If you have a data method that returns an object with the data (as you seem to have in the question), you can modify it like so:

const typeObj = array.reduce((obj, item) => {
  const { type, count } = item.data().specs;
  obj[type] = obj[type] || { count: 0 };
  obj[type].count += count;
  return obj;
}, {});
console.log(typeObj);