📝 Added sandbox (code sketchbook)

sandbox/for_comparisons/forin_vs_forof.js

@@ -0,0 +1,38 @@
+// https://stackoverflow.com/questions/29285897/what-is-the-difference-between-for-in-and-for-of-statements
+
+// heavily mutated array to demonstrate
+const arr = [3, 5, 7]
+arr['foo'] = "hello"
+arr.bar = 'there'
+arr[0] = 'what?'
+
+console.log('arr :=>', arr)
+
+console.log('for in loop...')
+for (const key in arr) {
+    console.log(key) // returns 0 1 2 foo
+}
+
+console.log('for in with key/value...')
+for (const key in arr) { // returns all key/val
+    const val = arr[key]
+    console.log('key :=>', key)
+    console.log('val :=>', val)
+}
+
+// for of is array specific
+console.log('for of loop...')
+for (const val of arr) {
+    console.log(val)
+    // returns 3 5 7 (not hello..., no key/value values)
+}
+
+// but can go over object.entries as it is an array
+console.log('for of with key/value...')
+for (const [key, val] of Object.entries(arr)) { // returns all key/val
+    console.log('key :=>', key)
+    console.log('val :=>', val)
+}
+
+// NOTE: for of can work with async calls whereas forEach cannot:
+// https://stackoverflow.com/questions/67739881/async-foreach-containing-array-pushvalue-not-working