add(server.tests.test2): 添加实验2的内容，将pdf里面标重要的进行提取出来

Server/tests/test2/important/reduce.js

@@ -0,0 +1,55 @@
+// arr.reduce(
+//     callback(accumulator, currentValue[, currentIndex[, array]])
+//     [, initialValue]
+// )
+
+const data1 = [1, 2, 3, 4, 5];
+// 没有使用初始值，则 sum 被初始为 1，cur从2开始, ..., ...
+let rst1 = data1.reduce((sum, cur) => {
+    return sum += cur
+})
+console.log(rst1)
+
+const data2 = [1, 2, 3, 4, 5];
+// 为初始值【1】，则temp被初始为【1】，cur从1开始, ..., ...
+let rst2 = data2.reduce((temp, cur) => {
+    return temp *= cur
+}, 1)
+console.log(rst2);
+
+const fruits = ['apple', 'banana', 'apple', 'banana', 'apple'];
+const rst3 = fruits.reduce((acc, cur) => {
+    if (!acc[cur])
+        acc[cur] = 1;
+    else
+        acc[cur]++;
+    return acc;
+}, {});
+console.log(rst3);
+
+const people = [
+    { name: 'zs', age: 25 },
+    { name: 'ls', age: 30 },
+    { name: 'ww', age: 25 },
+    { name: 'sb', age: 30 }
+];
+// 按年龄进行汇总，acc初始为{}，cur从zs这条数据开始
+const rst4 = people.reduce((acc, cur) => {
+    const age = cur.age;
+    if (!acc[age])
+        acc[age] = [];
+    acc[age].push(cur);
+    return acc;
+}, {});
+console.log(rst4);
+
+/*
+# node reduce.js 
+15
+120
+{ apple: 3, banana: 2 }
+{
+  '25': [ { name: 'zs', age: 25 }, { name: 'ww', age: 25 } ],
+  '30': [ { name: 'ls', age: 30 }, { name: 'sb', age: 30 } ]
+}
+*/