// Посчитать сумму по полю dimensions.width
 
const arr = [{
	{
		id: 1,
		dimensions: {
			width: 10,
			height: 20,
		},
	},
	{
		id: 2,
	},
	{
		dimensions: {
			width: 10,
			height: 15,
		},
	},
}]

function dimensionsWidth(arr) {
  const res = [];
 
  for (let name of arr) {
    if (typeof name?.dimensions?.width == "number") {
      res.push(name.dimensions.width);
    }
  }
 
  return res.reduce((acc, el) => {
    acc = acc + el;
    return acc;
  }, 0);
}
 
console.log(dimensionsWidth(arr));