add promise-all-custom

promise-all-custom.js

@@ -0,0 +1,42 @@
+// * This is a custom implementation of the Promise.all method
+
+function customPromiseAll(promises) {
+  return new Promise((resolve, reject) => {
+    if (promises.length === 0) {
+      resolve([])
+      return
+    }
+
+    const results = []
+    let completedPromises = 0
+
+    promises.forEach((promise, index) => {
+      Promise.resolve(promise)
+        .then((value) => {
+          results[index] = value
+          completedPromises++
+
+          if (completedPromises === promises.length) {
+            resolve(results)
+          }
+        })
+        .catch((error) => reject(error))
+    })
+  })
+}
+
+// ------------------------------------------------
+// Usage
+
+const promise1 = new Promise((resolve, reject) => {
+  setTimeout(() => resolve('Promise 1 resolved'), 200)
+})
+
+const promise2 = new Promise((resolve, reject) => {
+  setTimeout(() => resolve('Promise 2 resolved'), 300)
+})
+
+customPromiseAll([promise1, promise2]).then((values) => {
+  console.log(values)
+})
+// [ 'Promise 1 resolved', 'Promise 2 resolved']