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snippets/js/s/initialize-array-until.md

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+---
+title: Initialize array until
+type: snippet
+language: javascript
+tags: [array]
+author: chalarangelo
+cover: neon-desk-2
+dateModified: 2023-06-22T05:00:00-04:00
+---
+
+Initializes and fills an array with values generated by a function, until a condition is met.
+
+- Create an empty array, `arr`, an index variable `i` and an element `el`.
+- Use a `do...while` loop to add elements to the array, using the `mapFn` function, until the `conditionFn` function returns `true` for the given index `i` and element `el`.
+- The condition function, `conditionFn`, takes three arguments: the current index, the previous element and the array itself.
+- The mapping function, `mapFn`, takes three arguments: the current index, the current element and the array itself.
+
+```js
+const initializeArrayUntil = (conditionFn, mapFn) => {
+  const arr = [];
+  let i = 0;
+  let el = undefined;
+  do {
+    el = mapFn(i, el, arr);
+    arr.push(el);
+    i++;
+  } while (!conditionFn(i, el, arr));
+  return arr;
+};
+```
+
+```js
+initializeArrayUntil(
+  (i, val) => val > 10,
+  (i, val, arr) => (i <= 1 ? 1 : val + arr[i - 2])
+); // [1, 1, 2, 3, 5, 8, 13]
+```