Function that sums objects of the same shape

sum-objs.js

  // objs[] *must* be the same shape
  // returns new object with summation of all properties
  function sumObjs(objs) {
    const keys = Object.keys(objs[0]);
    // initialize return object with 0s
    const ret = keys.reduce((aggr, k) => { 
      aggr[k] = 0; 
      return aggr; 
    }, {});
    // sum each property
    return objs.reduce((aggr, obj) => {
      keys.forEach(k => {
        aggr[k] += obj[k];
      });
      return aggr;
    }, ret);
  }
  
  //e.g. sumObjs([ {a:2}, {a:3} ]) => {a:5}