Memory leak in Javascript

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Refs

1. Avoiding Memory Leaks in Node.js: Best Practices for Performance

What is a memory leak ?

Memory allocated but not freed.

What causes memory leak and how to resolve

Accidental global variable

Global variable is referenced by the root node(window or global this), they never gets garbage collected. This applies to all its relatives - variable/objects referenced by this global variable, and relatives of these variable/objects as well. This may construct a large graph.

Example:

// This will be hoisted as a global variable
function hello() {
  foo = "Message";
}
 
// This will also become a global variable as global functions have
// global `this` as the contextual `this` in non strict mode
function hello() {
  this.foo = "Message";
}

// This will also become a global variable as arrow functions
// do not have a contextual `this` and instead use a lexical `this`
const hello = () => {
    this.foo = 'Message";
}

Multiple references

One object referenced by multiple objects but one of the references never gets revoked.

Closures

When a closure holds a reference to a large object in heap, it keeps the object in memory as long as the closure is in use.

Timers and events

The use of setTimeout, setInterval, Observers and event listeners can cause memory leaks when heavy object references are kept in their callbacks without proper handling.