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javascript/snippets/join.md

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+---
+title: Join array into string
+type: snippet
+tags: [array]
+cover: couch-laptop
+dateModified: 2020-10-22T20:23:47+03:00
+---
+
+Joins all elements of an array into a string and returns this string.
+Uses a separator and an end separator.
+
+- Use `Array.prototype.reduce()` to combine elements into a string.
+- Omit the second argument, `separator`, to use a default separator of `','`.
+- Omit the third argument, `end`, to use the same value as `separator` by default.
+
+```js
+const join = (arr, separator = ',', end = separator) =>
+  arr.reduce(
+    (acc, val, i) =>
+      i === arr.length - 2
+        ? acc + val + end
+        : i === arr.length - 1
+          ? acc + val
+          : acc + val + separator,
+    ''
+  );
+```
+
+```js
+join(['pen', 'pineapple', 'apple', 'pen'],',','&'); // 'pen,pineapple,apple&pen'
+join(['pen', 'pineapple', 'apple', 'pen'], ','); // 'pen,pineapple,apple,pen'
+join(['pen', 'pineapple', 'apple', 'pen']); // 'pen,pineapple,apple,pen'
+```