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javascript/snippets/hash-browser.md

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+---
+title: Calculate SHA-256 hash (browser)
+type: snippet
+tags: [browser,promise]
+cover: padlocks
+dateModified: 2021-10-13T19:29:39+02:00
+---
+
+Creates a hash for a value using the [SHA-256](https://en.wikipedia.org/wiki/SHA-2) algorithm.
+Returns a promise.
+
+- Use the [SubtleCrypto](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto) API to create a hash for the given value.
+- Create a new `TextEncoder` and use it to encode `val`. Pass its value to `SubtleCrypto.digest()` to generate a digest of the given data.
+- Use `DataView.prototype.getUint32()` to read data from the resolved `ArrayBuffer`.
+- Convert the data to its hexadecimal representation using `Number.prototype.toString()`. Add the data to an array using `Array.prototype.push()`.
+- Finally, use `Array.prototype.join()` to combine values in the array of `hexes` into a string.
+
+```js
+const hashBrowser = val =>
+  crypto.subtle
+    .digest('SHA-256', new TextEncoder('utf-8').encode(val))
+    .then(h => {
+      let hexes = [],
+        view = new DataView(h);
+      for (let i = 0; i < view.byteLength; i += 4)
+        hexes.push(('00000000' + view.getUint32(i).toString(16)).slice(-8));
+      return hexes.join('');
+    });
+```
+
+```js
+hashBrowser(
+  JSON.stringify({ a: 'a', b: [1, 2, 3, 4], foo: { c: 'bar' } })
+).then(console.log);
+// '04aa106279f5977f59f9067fa9712afc4aedc6f5862a8defc34552d8c7206393'
+```