Add iterables tip

blog_posts/javascript-make-iterable.md

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+---
+title: "Tip: Make any JavaScript value iterable"
+type: tip
+tags: javascript,array,iterator,generator
+authors: chalarangelo
+cover: blog_images/colorful-plastic.jpg
+excerpt: Did you know you can define an iterator for any JavaScript value? This quick tip will show you how.
+---
+
+JavaScript's `Symbol.iterator` is a very powerful tool that every web developer should learn how to use. It allows you to define and customize the way a value is iterated, effectively allowing you to make any value iterable. You can easily apply this knowledge to plain JavaScript objects and even classes.
+
+All you need to correctly define an iterator is a generator function `yield`ing each of the iteration values. This could be used to retrieve key-value pairs in an object, call specific getter functions from a class or split a number into an array of digits:
+
+```js
+const obj = { a: 1, b: 2, c: 3 };
+
+obj[Symbol.iterator] = function* () {
+  for (let key of Object.keys(obj)) yield { [key]: obj[key] };
+};
+
+[...obj]; // [ { a: 1 }, { b: 2 }, { c: 3 }]
+
+class IterableNumber extends Number {
+  *[Symbol.iterator]() {
+    for (let digit of [...`${this}`].map(d => Number.parseInt(d))) yield digit;
+  }
+}
+
+const num = new IterableNumber(1337);
+[...num]; // [ 1, 3, 3, 7]
+```
+
+**Image credit:** [Paweł Czerwiński](https://unsplash.com/@pawel_czerwinski?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText) on [Unsplash](https://unsplash.com?utm_source=unsplash&utm_medium=referral&utm_content=creditCopyText)