reduce

var arr = [{"code":"111","num":1},{"code":"112","num":1},{"code":"111","num":3},{"code":"113","num":1},{"code":"113","num":5},{"code":"111","num":1}];
undefined
arr.reduce((o,i)=>{var {[i.code]:num=0}=o; return {...o, [i.code]: num+i.num};},{});
{111: 5, 112: 1, 113: 6}