<h1 id="heading-hoisted-regex-performance-optimization">Hoisted Regex Performance Optimization</h1>
In JavaScript, when you define a regular expression using the literal syntax (e.g., <code>/pattern/flags</code>), it's compiled where it's being defined.
If the regex is defined inside a function that is called multiple times, the regex compilation will occur each time the function is invoked. This repeated compilation can be costly, especially for complex regexes or frequently called functions.
To optimize, a common technique is to hoist the regex definition outside the function. This way, the regex is compiled only once when the script is loaded, and following function calls can reuse the same compiled regex instance.
<pre><code class="lang-js">// Unoptimized
function processString(str) {
 const regex = /pattern/flags;
 // ...
}

// Optimized
const regex = /pattern/flags;
function processString(str) {
 // ...
}
</code></pre>
In the optimized version, the regex is defined at the top level, outside the function scope. This ensures that the regex is compiled only once, improving performance for repeated function calls.
The trade off here is that the regex is now a global variable. It remains in memory for the lifetime of the script, which may not be desirable in some cases. However, the performance benefits of hoisting the regex can outweigh the memory considerations, especially for hot code (code that runs a lot).

# Hoisted Regex Performance Optimization

In JavaScript, when you define a regular expression using the literal syntax (e.g., `/pattern/flags`), it's compiled where it's being defined.

If the regex is defined inside a function that is called multiple times, the regex compilation will occur each time the function is invoked. **This repeated compilation can be costly, especially for complex regexes or frequently called functions.**

To optimize, **a common technique is to hoist the regex definition outside the function.** This way, the regex is compiled only once when the script is loaded, and following function calls can reuse the same compiled regex instance.

```js
// Unoptimized
function processString(str) {
  const regex = /pattern/flags;
  // ...
}

// Optimized
const regex = /pattern/flags;
function processString(str) {
  // ...
}
```

In the optimized version, the regex is defined at the top level, outside the function scope. This ensures that the regex is compiled only once, improving performance for repeated function calls.

The trade off here is that the regex is now a global variable. **It remains in memory for the lifetime of the script, which may not be desirable in some cases.** However, the performance benefits of hoisting the regex can outweigh the memory considerations, especially for hot code (code that runs a lot).

Regex Performance Optimization in JavaScript

Hoisted Regex Performance Optimization