JS代码压缩时布尔值切换原因：为何用!0、!1而非1、0？

Great question—this is a common point of confusion when looking at minified JavaScript, so let's break it down clearly.

First, let's establish the core equivalences here:

• !0 is exactly identical to true (since 0 is a falsy value, negating it returns the boolean true)
• !1 is exactly identical to false (since 1 is a truthy value, negating it returns the boolean false)

Now, why not just use 1 and 0 instead? Here are the key reasons:

1. Preserving Type Consistency #

Your original code defines useScroll as a boolean (true/false). If the minifier replaced those with 1/0, the variable would become a number instead. While loose equality (==) or basic condition checks (if (i)) would treat 1 like true and 0 like false, strict equality checks (===) would break entirely.

For example, if your code later included:

if (useScroll === true) {
  // Execute scroll-related logic
}

Using 1 instead of true would make this condition fail every time (since 1 === true evaluates to false). Minifiers prioritize keeping your code's logic intact, so preserving the original boolean type is critical to avoid subtle bugs.

2. No Length Advantage #

!0 and 1 are both 2 characters long; !1 and 0 are also 2 characters. There's no byte-saving benefit to using numbers over the negated falsy/truthy values, so the minifier doesn't gain anything by switching types.

3. Standard Minifier Behavior #

Tools like Terser or UglifyJS (the most common JS minifiers) default to this pattern because it's a safe, reliable way to compress boolean values without altering the code's underlying semantics. It's an industry convention that balances compression efficiency with compatibility.

To sum it up: using !0/!1 keeps your variable a boolean (matching the original code's intent) while achieving the same level of compression as using numbers. Using 1/0 would risk breaking strict equality checks down the line, which isn't worth the non-existent byte savings.

内容的提问来源于stack exchange，提问作者Sean T