How to sum the values of a JavaScript object?

A regular for loop is pretty concise:

var total = 0;

for (var property in object) {
    total += object[property];
}

You might have to add in object.hasOwnProperty if you modified the prototype.

You could put it all in one function:

function sum( obj ) {
  var sum = 0;
  for( var el in obj ) {
    if( obj.hasOwnProperty( el ) ) {
      sum += parseFloat( obj[el] );
    }
  }
  return sum;
}
    
var sample = { a: 1 , b: 2 , c:3 };
var summed = sum( sample );
console.log( "sum: "+summed );

function sum(obj) {
  return Object.keys(obj).reduce((sum,key)=>sum+parseFloat(obj[key]||0),0);
}
let sample = { a: 1 , b: 2 , c:3 };

console.log(`sum:${sum(sample)}`);

But this seems to be way slower: jsperf.com

If you're using lodash you can do something like

_.sum(_.values({ 'a': 1 , 'b': 2 , 'c':3 })) 

It can be as simple as that:

const sumValues = obj => Object.values(obj).reduce((a, b) => a + b);

Quoting MDN:

The Object.values() method returns an array of a given object's own enumerable property values, in the same order as that provided by a for...in loop (the difference being that a for-in loop enumerates properties in the prototype chain as well).

_{from Object.values() on MDN}

The reduce() method applies a function against an accumulator and each value of the array (from left-to-right) to reduce it to a single value.

_{from Array.prototype.reduce() on MDN}

You can use this function like that:

sumValues({a: 4, b: 6, c: -5, d: 0}); // gives 5

Note that this code uses some ECMAScript features which are not supported by some older browsers (like IE). You might need to use Babel to compile your code.