How to call reduce on an array of objects to sum their properties?

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A cleaner way to accomplish this is by providing an initial value as the second argument to reduce:

var arr = [{x:1}, {x:2}, {x:4}];
var result = arr.reduce(function (acc, obj) { return acc + obj.x; }, 0);
console.log(result);  // 7

The first time the anonymous function is called, it gets called with (0, {x: 1}) and returns 0 + 1 = 1. The next time, it gets called with (1, {x: 2}) and returns 1 + 2 = 3. It’s then called with (3, {x: 4}), finally returning 7.

This also handles the case where the array is empty, returning 0.

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