Bitwise operators in JavaScript are used for performance-sensitive tasks, binary data manipulation, and flag management. 1. 主要包括AND(&)、OR(|)、XOR(^)、NOT(~)、左移(>)和零填充右移(>>>)操作；2. 常用於高效設(shè)置標(biāo)誌位，例如通過按位或組合權(quán)限並用按位與檢查權(quán)限；3. 可加速整數(shù)運(yùn)算，如用左移代替乘法、右移代替除法；4. 在數(shù)據(jù)壓縮或編碼中用於提取或合併二進(jìn)制數(shù)據(jù)，如解析RGB顏色值；5. 需注意JavaScript使用有符號(hào)32位整數(shù)進(jìn)行操作，可能導(dǎo)致意外結(jié)果。

Bitwise operators in JavaScript might seem a bit obscure at first, especially if you're used to working with higher-level logic. But they have real-world uses, especially when dealing with performance-sensitive code, binary data, or flags.

JavaScript treats numbers as 32-bit integers when performing bitwise operations, which opens the door to manipulating individual bits directly. It's not something you'll use every day, but when you need it, it can be surprisingly helpful.

What Exactly Are Bitwise Operators?

Bitwise operators work on the binary representations of numbers—meaning they look at each individual bit (0 or 1) that makes up a number. Here are the most commonly used ones:

• & (AND): Returns a 1 in each bit position where both operands have a 1.
• | (OR): Returns a 1 in each bit position where either operand has a 1.
• ^ (XOR): Returns a 1 in each bit position where only one operand has a 1.
• ~ (NOT): Flips all the bits (turns 0 into 1 and vice versa).
• (Left shift): Shifts bits to the left, effectively multiplying by powers of two.
• (Sign-propagating right shift): Shifts bits to the right, keeping the sign.
• (Zero-fill right shift): Shifts bits to the right, filling new bits with zeros.

These aren't just for show—they let you do things like toggling specific bits or checking if a certain flag is set.

When Would You Use Them?

You probably won't reach for bitwise operators unless you're optimizing performance or dealing with low-level data structures. Here are some practical cases:

Checking or Setting Flags Efficiently

If you're managing multiple boolean states (like feature toggles or user permissions), using bits can save memory and improve speed. For example:

 const READ = 1; // 0001
const WRITE = 2; // 0010
const ADMIN = 4; // 0100

let userFlags = READ | WRITE;

// Check if user has write access
if (userFlags & WRITE) {
  // allow writing
}

This way, instead of storing multiple booleans, you store one integer that represents several options.

Fast Integer Math

Shifting bits can be faster than using Math.pow() or division. For example:

 x = x << 1; // same as x * 2
y = y >> 1; // same as Math.floor(y / 2)

This is particularly useful in game development or animation loops where performance matters.

Data Compression or Encoding

When dealing with binary formats like images, audio, or network protocols, bitwise operations help pack and unpack values efficiently. For instance, extracting RGB values from a 24-bit color code.

A Few Gotchas to Watch Out For

• JavaScript uses signed 32-bit integers for bitwise operations, so results might surprise you if you're expecting unsigned behavior.
• The ~ operator doesn't return a boolean—it flips all bits, which often leads to negative numbers.
• Don't overuse them. Unless performance or space is critical, regular logic is usually more readable.

They're not always needed, but knowing how and when to use bitwise operators gives you another tool for optimization and handling binary-style data. If you're working with flags, doing math-heavy tasks, or dealing with binary formats, they can come in handy.

基本上就這些。

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