JavaScript Memory and Garbage Collection

Find out what keeps an object alive, why apps leak memory, and how the browser cleans up without freezing the page.

Lessons

Steps

About 1 hour

Duration

Your own

Pace

Prefer video?

Curriculum

01
Stack vs heap
The stack runs your code. The heap holds your data.
02
References and the object graph
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An object stays alive as long as something can reach it.
03
GC roots and reachability
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If a root can reach it, it stays alive.
04
Young generation and minor GC
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Most objects die young, so only the survivors cost anything.
05
Major GC: mark, sweep, compact
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How V8 cleans the old generation in three steps.
06
How GC avoids freezing the page
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Four ways to schedule GC work, measured against a 16 ms frame.
07
How memory leaks happen
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The component left. Its data didn't.
08
Weak references and WeakMap
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A reference that doesn't keep objects alive.
09
Finding leaks with heap snapshots
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Snapshot, repeat, compare, then follow the retainers.