Adding up the values of an array of objects javascript

Question

I have an array of objects like this : const array=[{a:1, b:1} , {a:2, b:3} ,{a:1, b:1}]

i want an array like results = [{a:4 , b:5}] which is the sum of all values from the array of objects according to the key .

I tried something like this but sometimes it skipping the 1st object in the array :

       array.reduce((acc, n) => {
          for (var prop in n) {
            if (acc.hasOwnProperty(prop)) acc[prop] += n[prop];
            else acc[prop] = 0;
          }
          return acc;
        }, {})

Answer 1

You need to initialize acc before assigning, so small modification below will work

 const array=[{a:1, b:1} , {a:2, b:3} ,{a:1, b:1}]
 const res = array.reduce((acc, n) => {
          for (var prop in n) {
          acc[prop] = acc[prop] || 0; // Need to initialize before assigning
            if (n.hasOwnProperty(prop)) {
                 acc[prop] += n[prop];
               } 
          }
          return acc;
        }, {})
console.log(res);