E-commerce and cloud-computing company Amazon.com (AMZN 1.60%) recently wrapped up its 2018 books, reporting fourth-quarter and full-year results on the last day of January. While the important fourth-quarter revenue and earnings per share metrics included in the update are worth considering, investors can also use the annual update as a time to reflect on what the company accomplished over the entire year of 2018.

When looking at Amazon's full-year 2018 performance, it's clear why the stock has performed so well over the last 12 months. Here's a look at some of the biggest takeaways from Amazon's 2018 performance.

Amazon Echo Dot sitting on a table next to a lamp

Amazon Echo Dot. Image source: Amazon.com.

1. Net sales of $232.9 billion

Amazon's total net sales across its wide-reaching business increased 31% year over year to an impressive $232.9 billion. To put Amazon's size in perspective, this is equal to nearly half of Walmart's (WMT -0.15%) $511.9 billion of trailing-12-month revenue. 

Notably, Amazon's 31% year-over-year revenue growth was equal to the 31% revenue growth Amazon posted in 2017. But the company's revenue growth did decelerate toward the end of the year, with fourth-quarter revenue rising 20% year over year.

2. Net income of $10.1 billion

The e-commerce and cloud-computing company's net income soared, rising from $3 billion in 2017 to $10.1 billion in 2018. On a per-share basis, this translates to earnings per share of $6.15 in 2017 and $20.14 in 2018.

This net income crushed Walmart's, proving Amazon's business model is superior. Walmart's trailing-12-month net income was $5.7 billion.

3. North America operating income of $7.3 billion

While Amazon Web Services (AWS), the company's lucrative cloud-computing business, was expected to see its profits surge in 2018, the company's North America segment (which excludes AWS sales in the region) surprised to the upside. North America operating income surged 156% higher in 2018, rising from $2.8 billion in 2017 to $7.3 billion in 2018.

This is impressively in line with AWS's operating income, which was also at $7.3 billion in 2018. With Amazon's North America segment largely driven by the company's e-commerce sales, such strong growth in the segment's operating income vouches for the scalability of Amazon's massive retail business.

4. 80,000 Alexa skills

Amazon's domination in the smart-speaker market persisted in 2018, helped by refreshed versions of its Echo Dot, Echo Plus, and Echo Show, as well as other entirely new Alexa-enabled devices. The proliferation of its voice-assistant technology, Alexa, was also helped by its adoption on many new third-party devices. With the help of both surging sales of third-party and Amazon-branded Alexa-enabled devices, the number of devices with Alexa built-in more than doubled last year compared to 2017.

Check out the latest Amazon earnings call transcript.

Also highlighting Amazon's strong momentum in the smart-speaker market was optimism from developers, evidenced by the 80,000 Alexa skills now available on the devices. This is up from 30,000 skills around the end of 2017.

When we review these metrics from 2018, it's no surprise that Amazon's stock crushed the S&P 500 over the last 12 months, rising 11% year over year while the S&P 500 gained just 1.6%.