Chapter VIII · Arrays
filter
The filter method creates a shallow copy of a portion of a given array containing only elements that pass a test condition.
01 How It Works
Think of a security checkpoint gate allowing only items meeting specific criteria to pass.
The callback returns a boolean; truthy values keep the item, falsy values discard it.
example.js
const nums = [1, 2, 3, 4];
const evens = nums.filter(n => n % 2 === 0); // [2, 4]1. Call .filter() on an array.
2. Supply a condition test callback function.
3. Collect matching elements into a new filtered array.
02 Practical Example
Here is how you might see this concept applied in real-world code:
practical.js
const scores = [45, 80, 65, 90];
const passed = scores.filter(s => s >= 60);Key Takeaway
Filter extracts subsets of data matching specific boolean conditions.