createHash
- Node.js course
- Intermediate
- Lesson 101/116
- 5 min
Learn to create hashes with crypto.createHash.
createHash
crypto.createHash(algorithm) creates a hash generator. You feed data with update(data) and take the hash with digest(format). Chaining is common.
Example: crypto.createHash("sha256").update("hello").digest("hex"). "sha256" is the algorithm; "hex" is the output format (hexadecimal). Other formats: "base64" gives a shorter string; "latin1" is rarer. update() can be called multiple times; data is concatenated. After digest() the generator cannot be reused. SHA-256 output is always 64 hex characters (256 bits = 32 bytes). For password storage sha256 alone is not enough; salt and slow algorithms are needed.
update and digest
update() can feed data piece by piece. For large files you stream data in; you use less memory. digest() finalizes and returns the hash.
Example: const h = crypto.createHash("sha256"); h.update("part1"); h.update("part2"); h.digest("hex");. This gives the same hash as update("part1part2") because data is concatenated. digest("hex") returns a hex string; digest("base64") a shorter string. After calling digest() calling update() throws; the generator is single-use. To hash the same data again you need a new createHash call. This is why chaining is practical: it finishes all steps in one line.
Practice Hash a string with SHA-256
Import with const crypto = require("node:crypto");. Get a hash with const hash = crypto.createHash("sha256").update("merhaba").digest("hex");. Print the first 16 characters with console.log(hash.slice(0, 16)).
Starter code
// Import the crypto module
// write here
// Hash "merhaba" with SHA-256
// write here
// Print the first 16 characters
// write hereSample solution
const crypto = require("node:crypto");
const hash = crypto.createHash("sha256").update("merhaba").digest("hex");
console.log(hash.slice(0, 16));Expected output
4c6bcdd55f3153e1
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Complete the createHash call
const hash = crypto.____("sha256").update("merhaba").digest("hex");const hash = crypto.createHash("sha256").update("merhaba").digest("hex");Explanation: createHash with sha256 creates a hash generator.
2 Match each step to its function
| Term | Meaning |
|---|---|
createHash |
Creates generator |
update |
Feeds data |
digest |
Finalizes hash |
"hex" |
Hexadecimal format |
3 What kind of value does digest("hex") return?
crypto.createHash("sha256").update("x").digest("hex")- A hexadecimal string Correct answer
- A binary buffer
- A number
- Date nesnesi
Explanation: The hex format gives a hex string.