Map, Filter, Reduce, and Function Composition
Methods such as map, filter, and reduce are higher-order operations over collections. map transforms every element, filter selects elements, and reduce combines values into an accumulator. They are not merely shortcuts; they express different computational intentions.
Composition becomes especially useful when small pure functions are combined into larger transformations.
A Collection Pipeline
const numbers = [1, 2, 3, 4, 5, 6];
const result = numbers
.filter(n => n % 2 === 0)
.map(n => n * n)
.reduce((sum, n) => sum + n, 0);
console.log(result);💡 The pipeline first selects even values, then squares them, and finally sums the resulting values.
Key Takeaways
- map transforms elements.
- filter selects elements.
- reduce models accumulation into one result.
Knowledge Check
Which method is most directly intended to transform every element into another value?