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snippets/js/s/flatten-object.md

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+---
+title: Flatten object
+type: snippet
+language: javascript
+tags: [object,recursion]
+cover: lighthouse
+dateModified: 2020-10-19T18:51:03+03:00
+---
+
+Flattens an object with the paths for keys.
+
+- Use recursion.
+- Use `Object.keys()` combined with `Array.prototype.reduce()` to convert every leaf node to a flattened path node.
+- If the value of a key is an object, the function calls itself with the appropriate `prefix` to create the path using `Object.assign()`.
+- Otherwise, it adds the appropriate prefixed key-value pair to the accumulator object.
+- You should always omit the second argument, `prefix`, unless you want every key to have a prefix.
+
+```js
+const flattenObject = (obj, prefix = '') =>
+  Object.keys(obj).reduce((acc, k) => {
+    const pre = prefix.length ? `${prefix}.` : '';
+    if (
+      typeof obj[k] === 'object' &&
+      obj[k] !== null &&
+      Object.keys(obj[k]).length > 0
+    )
+      Object.assign(acc, flattenObject(obj[k], pre + k));
+    else acc[pre + k] = obj[k];
+    return acc;
+  }, {});
+```
+
+```js
+flattenObject({ a: { b: { c: 1 } }, d: 1 }); // { 'a.b.c': 1, d: 1 }
+```