JavaScript Functions
Write reusable logic.
On this page
The concept
Functions accept arguments and return results. An arrow function is a concise way to express a small function.
Code example
JavaScript
const average = values => values.reduce((a, b) => a + b, 0) / values.length;
console.log(average([82, 91, 76, 95]));Output
86
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1
const average = values => values.reduce((a, b) => a + b, 0) / values.length;2
console.log(average([82, 91, 76, 95]));Follow the example
Start to inspect the source, values, and output. These prepared steps explain the published sample; grouped loop steps describe multiple iterations.
View the complete dry-run table
| Step / line | What happens | State after step | Output so far |
|---|---|---|---|
| Create the average function; its body has not run yet. | — | — | |
| Pass four values into average. reduce sums them to 344, then divide by 4. | return = 86 | 86 |
Behind the scenes
How JavaScript processes this code
A JavaScript engine parses and runs the source. A function body runs when the function is called. console.log writes to the console.