Editing Functional programming (section)

=== Imperative vs. functional programming ===

The following two examples (written in [[JavaScript]]) achieve the same effect: they multiply all even numbers in an array by 10 and add them all, storing the final sum in the variable <code>result</code>.

Traditional imperative loop:
<syntaxhighlight lang="javascript">
const numList = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
let result = 0;
for (let i = 0; i < numList.length; i++) {
  if (numList[i] % 2 === 0) {
    result += numList[i] * 10;
  }
}
</syntaxhighlight>

Functional programming with higher-order functions:
<syntaxhighlight lang="javascript">
const result = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
               .filter(n => n % 2 === 0)
               .map(a => a * 10)
               .reduce((a, b) => a + b, 0);
</syntaxhighlight>Sometimes the abstractions offered by functional programming might lead to development of more robust code that avoids certain issues that might arise when building upon large amount of complex, imperative code, such as [[off-by-one error]]s (see [[Greenspun's tenth rule]]).