Run results for: add objects on loop

Test name	Executions per second
✓ spread	810 Ops/sec
mutable assign	339 Ops/sec
assign	205 Ops/sec
lodash merge	29 Ops/sec

assign

const BASE_OBJECTS = (() => {
  const arr = new Array(10000);
  for (let i = 0; i < 10000; i++) {
    arr[i] = {
      id: i,
      name: "obj_" + i,
      value: i * 2,
      active: i % 2 === 0
    };
  }
  return arr;
})();


let result;

for (let round = 0; round < 10; round++) {
  result = new Array(BASE_OBJECTS.length);

  for (let i = 0; i < BASE_OBJECTS.length; i++) {
    result[i] = Object.assign(
      {},
      BASE_OBJECTS[i],
      {
        extra1: i,
        extra2: i + 1,
        extra3: i + 2
      }
    );
  }
}

spread

const BASE_OBJECTS = (() => {
  const arr = new Array(10000);
  for (let i = 0; i < 10000; i++) {
    arr[i] = {
      id: i,
      name: "obj_" + i,
      value: i * 2,
      active: i % 2 === 0
    };
  }
  return arr;
})();

let result;

for (let round = 0; round < 10; round++) {
  result = new Array(BASE_OBJECTS.length);

  for (let i = 0; i < BASE_OBJECTS.length; i++) {
    result[i] = {
      ...BASE_OBJECTS[i],
      extra1: i,
      extra2: i + 1,
      extra3: i + 2
    };
  }
}

mutable assign

const BASE_OBJECTS = (() => {
  const arr = new Array(10000);
  for (let i = 0; i < 10000; i++) {
    arr[i] = {
      id: i,
      name: "obj_" + i,
      value: i * 2,
      active: i % 2 === 0
    };
  }
  return arr;
})();


let result;

for (let round = 0; round < 10; round++) {
  result = new Array(BASE_OBJECTS.length);

  for (let i = 0; i < BASE_OBJECTS.length; i++) {
    result[i] = Object.assign(
      BASE_OBJECTS[i],
      {
        extra1: i,
        extra2: i + 1,
        extra3: i + 2
      }
    );
  }
}

lodash merge

const BASE_OBJECTS = (() => {
  const arr = new Array(10000);
  for (let i = 0; i < 10000; i++) {
    arr[i] = {
      id: i,
      name: "obj_" + i,
      value: i * 2,
      active: i % 2 === 0
    };
  }
  return arr;
})();


let result;

for (let round = 0; round < 10; round++) {
  result = new Array(BASE_OBJECTS.length);

  for (let i = 0; i < BASE_OBJECTS.length; i++) {
    result[i] = _.merge({},
      BASE_OBJECTS[i],
      {
        extra1: i,
        extra2: i + 1,
        extra3: i + 2
      }
    );
  }
}