Memory leaks

Learn memory leak detection and prevention.

Memory leak

A memory leak is when objects no longer in use are kept in memory. A common cause is a cache that keeps growing. Objects are added but never removed; the cache grows forever.

A detectLeak(cache, limit) function checks this: it returns true if cache.size > limit. Example: with new Set(['x', 'y', 'z']), detectLeak(cache, 2) returns true (3 > 2). detectLeak(cache, 10) returns false (3 < 10). This model checks whether a cache has crossed a limit. In a real application watching cache growth is how you catch a leak early. Set.size gives the number of elements in a set.

Leak detection

In this lesson we write the detectLeak function. The function takes a cache and a limit; it returns true if the cache has crossed the limit. This is a simple way to catch a memory leak with a size check.

Example: const cache = new Set(['x', 'y', 'z']). detectLeak(cache, 2) returns true (3 > 2). detectLeak(cache, 10) returns false. cache.size gives the element count of the set; it is compared with > limit. This pattern is used in real applications to watch cache growth: a limit is set, an alert fires when crossed. The output is true and false; deterministic.

Exercise Write the leak detector

Write function detectLeak(cache, limit). Return cache.size > limit. Define const cache = new Set(['x', 'y', 'z']). Print console.log(detectLeak(cache, 2)) and console.log(detectLeak(cache, 10)).

Show example solution

function detectLeak(cache, limit) {
  return cache.size > limit;
}
const cache = new Set(['x', 'y', 'z']);
console.log(detectLeak(cache, 2));
console.log(detectLeak(cache, 10));

Test yourself

What does new Set(['x','y','z']).size return?
```
new Set(['x','y','z']).size
```
- 2
- 3
- 1
- 0
Show answer

3 — The set has three elements: x, y, z.
Match each concept to its description

Memory leak

Unused objects remain
Set.size

Element count
limit

Boundary
cache

Cache

Complete the size comparison

return cache.____ > limit;

Show answer

return cache.size > limit;

Next lesson: Heap snapshot

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