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+/** example file
+ * 
+ * this script tests async chain handling;
+ * runnig async functions sequentialy
+ * or running in parallel
+ * 
+ */
+
+
+/**
+ * functions a and b are asyncohronus
+ */
+
+async function a(msg) {
+    sum = 0;
+    for (i=0 ; i< parseInt(Math.floor(Math.random() * 1000000000)); i++) {
+        sum += i;
+    }
+    console.log(msg, sum);
+    return sum
+}
+
+async function b(upto) {
+    sum = 0;
+    for (i=0 ; i< upto; i++) {
+        sum += i;
+    }
+    console.log(upto, sum);
+    return new Promise((resolve, reject) => { resolve(sum); });
+}
+
+
+/** test
+ * --- -- -- - - -
+ * is an asynchronous function
+ * that calls multiple times in parallel
+ * the a and b functions
+ */
+async function test() {
+    labels = ['one', 'two', 'three', 'four', 'five'];
+    labels.forEach( lab => { 
+        a(lab)
+    });
+    console.log('test1');
+
+    limits = [1000000, 50000, 30000000, 500, 8];
+    limits.forEach( lim => {
+        b(lim).then(console.log(lim,'is done!'));
+    });
+    console.log('test2');
+}
+
+
+test()  // run test (many async functions in parallel)
+.then(() => {   // after test is ended
+    console.log('test parts(1+2) ended');
+
+    // run async functions in sequentialy
+    a('more')
+    .then(() => {
+        b(100000)
+        .then(() => {
+            a('last')
+            .then(() => {
+                b(20)
+                .then(() =>{
+                    console.log('exiting...');
+                    console.log('\n\n--------------------\nNext please...\n--------------------\n\n');
+                })
+            });
+        });
+    });
+
+});
+
+
+
+/**
+ * xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+ * -----------------------------------------------------------------------------
+ * 
+ * * * * * * * * * * * *   S E C O N D   E X A M P L E   * * * * * * * * * * * *
+ * 
+ * -----------------------------------------------------------------------------
+ * xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
+ */
+
+
+/** sleep
+ * --- -- -- - - -
+ * an async function with predictable waiting time
+ */
+async function sleep(time = 1) {
+	const sleepMilliseconds = time * 1000;
+        return new Promise((resolve, reject) => {
+            setTimeout(() => {
+                console.log(`Slept for: ${sleepMilliseconds}ms`);
+                resolve(sleepMilliseconds);
+            }, sleepMilliseconds);
+        });
+}
+
+// run all in parallel
+Promise.all([   // after each call is completed
+                // '.then(...)' make a message note
+    sleep(3).then(()=>{ console.log('instance', 3, 'completed')}),
+    sleep(2).then(()=>{ console.log('instance', 2, 'completed')}),
+    sleep(1).then(()=>{ console.log('instance', 1, 'completed')})
+
+])
+.then( () => {  // then 
+    console.log('Now, there should be all done!', 'DONE!')
+});
+
+
+// message to test that async functions keep running on the background
+console.log('--> is this the end?', 'NOPE! <--');
+