Common types of JavaScript memory leaks include: 1. Unexpected global variables, which can be prevented by using strict mode; 2. Uncleaned event listeners should be explicitly unbinded or rely on framework lifecycle management; 3. Leaks caused by closure references to avoid holding large objects for a long time and manually dereferences; 4. For forgotten timers or callbacks, the timer needs to be cleared and the cleaning function is returned in useEffect; 5. DOM node cyclic references, which are alleviated by modern browsers but still need to be paid attention to. Detection methods include: 1. Use the heap snapshot of Chrome DevTools to compare object growth; 2. Use the Performance panel to monitor memory metric changes; 3. Use the performance.memory API to monitor memory usage in the code; 4. Use WeakMap/WeakSet to reduce the reference strength to avoid leakage. The prevention strategy is: ? Unbind events and timers in time ? Avoid global variables ? Use closures with caution ? Store auxiliary data with WeakMap/WeakSet ? Clean resources with the framework life cycle ? Regular memory snapshot analysis. Development suggestions include simulating long-term operations, automated memory detection and independent testing of high-frequency objects. Regular memory usage checks can effectively prevent accumulated performance problems and improve user experience.

Although JavaScript memory leaks do not explicitly expose pointer problems like C/C, they may still lead to performance degradation or even page crashes in long-term running web applications, especially single-page applications (SPA). Understanding common leak patterns and mastering detection and prevention strategies is a skill that front-end developers must master.

1. Common JavaScript memory leak types

1. Unexpected global variables

When a variable is assigned without being declared, it will automatically become a property of the global object ( window ) and reside in memory for a long time.

 function leakyFunction() {
  leakedVariable = "I'm global now"; // Forgot to use var/let/const
}

Prevention methods :

• Use strict mode ( 'use strict' ) to make such errors throw exceptions.
• Avoid operating undeclared variables directly inside functions.

2. Uncleaned event listener

After the DOM element is removed, if the event listener is not removed, its callback function may still hold a reference to the DOM, which cannot be recycled.

 const button = document.getElementById('btn');
button.addEventListener('click', handleClick);
// The subsequent remove button, but not the remove listener

Solution :

• Use removeEventListener to explicitly unbind.
• Or use once: true option (one-time listening).
• In modern frameworks (such as React/Vue), the life cycle management of the framework is dependent on.

3. Leaks caused by closure references

Closures retain references to external variables, and if the reference is not released, it may cause a large amount of data to reside in memory.

 function outer() {
  const hugeData = new Array(1000000).fill('data');
  return function inner() {
    console.log('Still referencing hugeData');
  };
}
const fn = outer(); // hugeData cannot be recycled

suggestion :

• Avoid holding large objects in closures for a long time.
• Manually dereference after use: fn = null .

4. Forgotten timer or callback

The external object is referenced in the callback of setInterval or setTimeout , and the timer is not cleared.

 setInterval(() => {
  const data = fetchData();
  document.getElementById('container').innerText = data;
}, 1000);

If the timer is not cleared after page switching or component destruction, data and DOM nodes may continue to consume memory.

solve :

• Record the timer ID and call clearInterval / clearTimeout at the appropriate time.
• Use the cleanup function of useEffect in React:

 useEffect(() => {
  const timer = setInterval(fetchData, 1000);
  return () => clearInterval(timer);
}, []);

5. Circular references of DOM nodes (old IE problem, modern browsers have alleviated)

Although modern garbage collectors (such as V8) can handle circular references, they still need to be paid attention to in some scenarios.

 const element = document.getElementById('box');
element.someProperty = element; // Self-reference

2. How to detect JavaScript memory leaks

1. Use Chrome DevTools' Memory Panel

• Heap Snapshot :

  • Open DevTools → Memory → Heap Snapshot
  • Take snapshots of multiple time points and compare the number of objects
  • Find constructors that grow abnormally (such as Array , Closure , Detached DOM Tree )

• Record Allocation Timeline :

  • Observe memory allocation in real time
  • You can locate specific code lines to find out the problems that short-term objects are not recycled.

2. Use the Performance panel to monitor memory usage

• Open the Performance panel and check Memory
• Record user operation process
• Observe whether indicators such as JS heap memory, number of DOM nodes, number of listeners continue to rise

3. Monitor memory usage (in code)

 // Only available in Chrome if (performance.memory) {
  console.log(performance.memory);
  // { usedJSHeapSize, totalJSHeapSize, jsHeapSizeLimit }
}

Can be used for automated monitoring or abnormal alarms.

4. Use WeakMap/WeakSet to reduce citation intensity

• Keys in WeakMap and WeakSet are weak references and will not prevent garbage collection
• Suitable for scenarios where data is associated but does not want to affect life cycles

 const cache = new WeakMap();
const domElement = document.getElementById('myDiv');
cache.set(domElement, { tooltip: 'info' }); // After domElement is removed, the cache will automatically fail

3. Summary of prevention strategies

• ? Timely unbinding event listeners and timers
• ?Avoid unexpected global variables (using strict mode)
• ? Use closures with caution to avoid holding large objects for a long time
• ?Storage auxiliary data using WeakMap/WeakSet
• ? Clean up resources using life cycle hooks in the framework
• ?During memory snapshot analysis regularly, especially after complex interactions

4. Development suggestions

• Simulate long-term operations of users in the development environment (such as repeatedly opening/closing modal boxes)
• Automated memory detection using Puppeteer or Cypress with DevTools protocol
• Perform independent memory tests on frequently created and destroyed objects (such as charts, editors)

Basically that's it. Memory leaks do not always appear immediately, but they can seriously affect the user experience when accumulated. Develop the habit of checking memory regularly, which is much more efficient than troubleshooting after problems occur.

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