7 Lesser-Known JavaScript String Contains Methods That Outperform includes()

I was recently grappling with a performance bottleneck in a legacy JavaScript module. It was a classic case: heavy string manipulation inside a tight loop, and the culprit, almost predictably, was `String.prototype.includes()`. Now, don't get me wrong, `includes()` is wonderfully readable—a modern staple for checking substring existence. But readability often comes at a cost, especially when we're talking about millions of iterations. I started to wonder, are we, as developers building increasingly sophisticated frontends and Node services, blindly accepting the default method simply because it’s the most recent addition to the standard library? My curiosity piqued; I suspected there were older, less celebrated, or perhaps more specialized methods lurking in the JavaScript specification that might offer a measurable speed advantage when raw performance is the objective, not just semantic clarity.

This line of questioning led me down a rabbit hole of benchmarking and specification diving, moving away from the comfortable surface level of modern ES6 features. We often forget that the language has decades of history informing how basic operations are executed under the hood by various engine implementations like V8 or SpiderMonkey. If we are optimizing for speed in critical path code, we must treat these built-in methods not as equivalents, but as distinct algorithmic choices with different performance profiles. Let's look beyond the obvious and examine seven specific string containment checks that, in certain contexts, consistently edged out `includes()` in my early tests.

The first alternative that warrants serious consideration is the venerable `String.prototype.indexOf()`. This method returns the index of the first occurrence or `-1` if not found. Because it returns a numeric index, the comparison required is a simple numeric check (`!== -1`), which historically has been marginally faster than the boolean coercion path often taken by `includes()` in older engine versions, though modern JIT compilers are closing that gap rapidly. I found that in scenarios involving very long strings where the substring is expected near the beginning, `indexOf()` maintains a slight edge because it immediately provides positional data that the engine can optimize around. Furthermore, if you need to know *where* the match occurs for subsequent processing, using `indexOf()` saves you an extra function call to find the position later, making it a dual-purpose win. Another strong contender, often overlooked due to its slightly arcane nature, is `String.prototype.search()`, which accepts a regular expression argument. While using a regex for a simple literal string match seems like overkill—and indeed, it usually is slower for fixed strings due to regex engine overhead—it shines when the containment check needs to be case-insensitive or pattern-based without constructing a new string instance for case conversion first.

Shifting focus slightly, we move into methods that perform substring matching but aren't strictly boolean checks, yet can be coerced into one. Consider `String.prototype.match()`, which, when used with a non-global regex, returns an array-like object upon success or `null` on failure. Checking for existence here becomes a simple truthiness test against the returned value. I observed that when the substring being searched for is complex enough to warrant a regex anyway, `search()` and `match()` become functionally similar to `includes()`, but their underlying implementation might use different internal search algorithms depending on whether the regex is anchored or not. Then there’s the often-forgotten `String.prototype.lastIndexOf()`, which, surprisingly, can outperform `indexOf()` if you are searching for a substring that is much more likely to appear near the *end* of the target string, as the engine starts its traversal from the right boundary. For true low-level grit, we have `String.prototype.charCodeAt(index)` combined with a manual loop comparing character codes, which, while verbose and requiring meticulous bounds checking, bypasses all higher-level string searching abstractions entirely, offering maximum control over the iteration process, albeit rarely necessary today. Finally, I looked at `String.prototype.slice()` combined with comparison, though this is purely academic for simple containment: you slice a segment equal to the search term and compare it directly. This only wins if the engine's optimization for slicing and comparison is superior to its optimized substring search routine for extremely short search terms, a niche case where I saw fleeting advantages in micro-benchmarks.

Let's pause for a moment and reflect on that collection: `indexOf()`, `search()`, `lastIndexOf()`, `match()`, and the character-by-character manual check, plus two others related to substring extraction and comparison. The takeaway isn't that any single one universally replaces `includes()`. Rather, it’s that the performance profile is highly dependent on the context: string length, expected match location, and whether pattern matching is involved. If I am scanning a 10-megabyte log file for an error code that almost always appears in the first kilobyte, `indexOf()` is my first port of call. If I need to check for the presence of a word regardless of case without changing the original string, `string.search(/word/i)` is cleaner and potentially faster than `string.toLowerCase().includes('word')`. The performance difference between these methods is often measured in nanoseconds, but when these operations occur millions of times per second in a high-throughput service, those nanoseconds accumulate into noticeable latency. It's about choosing the right tool for the specific mechanical job, rather than defaulting to the one with the nicest syntax.