**`Zlib`** is a built-in module in Node.js that provides decompression or compression properties on strings and buffers in a program.

The **`zlib.constants`** include dozens of operations that we do not need to include separately in our program. Those operations include:

- Flush values
- Return codes for compression and decompression functions
- The deflate compression method
- Initializing `zalloc`, `zfree`, and `opaque`
- Compression strategy
- Compression levels

These constant operations are pre-loaded every time we include the `zlib.constant` in our program.

# Syntax

As stated above, we do not need to define the constants by ourselves. The basic syntax of constant operations is as follows:

``` node.js
#define Z_NO_FLUSH 
#define Z_STREAM_END
#define Z_NO_COMPRESSION
#define Z_BINARY
```

# Code

For better understanding, observe the following code illustration.

const zlib = require("zlib");

console.log("Values for constants:")
console.log("Z_NO_FLUSH: ", zlib.constants.Z_NO_FLUSH)
console.log("Z_STREAM_END: ", zlib.constants.Z_STREAM_END)
console.log("Z_MEM_ERROR: ", zlib.constants.Z_MEM_ERROR)
console.log("Z_BUF_ERROR: ", zlib.constants.Z_BUF_ERROR)
console.log("Z_NO_COMPRESSION: ", zlib.constants.Z_NO_COMPRESSION)
console.log("Z_DEFAULT_STRATEGY: ", zlib.constants.Z_DEFAULT_STRATEGY)


# Explanation

The above code prints the levels for constants used in the example. `zlib` module is imported in the program by typing `const zlib = require("zlib");.`

How to use 'zlib constants' in Node.js

Syntax

Code

Explanation