finished homework SunJieMing#4

exercises.js

@@ -4,27 +4,56 @@ function multiplyArguments() {
   // use the arguments keyword to multiply all of the arguments together and return the product
   // if no arguments are passed in return 0
   // if one argument is passed in just return it
+  var total = 1;
+  if (arguments.length > 0) {
+    for (var i = 0; i < arguments.length; i++) {
+      total *= arguments[i];
+    }
+    return total;
+  } else {
+    return 0;
+  }
 }
 
 function invokeCallback(cb) {
   // invoke cb
+  cb();
 }
 
 function sumArray(numbers, cb) {
   // sum up all of the integers in the numbers array
   // pass the result to cb
   // no return is necessary
+  var result = 0;
+  for (var i = 0; i < numbers.length; i++) {
+    result += numbers[i];
+  }
+  cb(result);
 }
 
 function forEach(arr, cb) {
   // iterate over arr and pass its values to cb one by one
   // hint: you will be invoking cb multiple times (once for each value in the array)
+  for (var i = 0; i < arr.length; i++) {
+    cb(arr[i]);
+  }
 }
 
 function map(arr, cb) {
   // create a new array
   // iterate over each value in arr, pass it to cb, then place the value returned from cb into the new arr
   // the new array should be the same length as the array argument
+  var newArr = arr.map(function(num) {
+    return cb(num);
+  });
+  /*for (var i = 0; i < arr.length; i++) {
+    newArr.push(cb(arr[i]));
+  }*/
+  // arr.forEach( function(num) {
+  //   newArr.push(cb(num));
+  // });
+
+  return newArr;
 }
 
 function getUserConstructor() {
@@ -34,25 +63,47 @@ function getUserConstructor() {
   // the constructor should have a method 'sayHi' on its prototype that returns the string 'Hello, my name is {{name}}'
   // {{name}} should be the name set on each instance
   // return the constructor
+  function User(options) {
+    this.username = options.username;
+    this.name = options.name;
+    this.email = options.email;
+    this.password = options.password;
+    this.sayHi = function() {
+      return 'Hello, my name is ' + this.name;
+    };
+  }
+  return User;
 }
 
 function addPrototypeMethod(Constructor) {
   // add a method to the constructor's prototype
   // the method should be called 'sayHi' and should return the string 'Hello World!'
+  Constructor.prototype.sayHi = function() {
+    return 'Hello World!';
+  };
 }
 
 function addReverseString() {
   // add a method to the string constructor's prototype that returns a reversed copy of the string
   // name this method reverse
   // hint:
   // you will need to use 'this' inside of reverse
+  var result = '';
+  String.prototype.reverse = function() {
+    for (var i = 0; i < this.length; i++) {
+      result = this[i] + result;
+    }
+    return result;
+  };
 }
 
 function nFactorial(n) {
   // return the factorial for n
   // solve this recursively
   // example:
   // the factorial of 3 is 6 (3 * 2 * 1)
+if (n === 2) return 2;
+return n * nFactorial(n-1);
 }
 
 function cacheFunction(cb) {
@@ -67,6 +118,27 @@ function cacheFunction(cb) {
   // if the function you return is invoked with 5 it would pass 5 to cb(5) and return 25
   // if the function you return is invoked again with 5 it will look on an object in the closure scope
   // and return 25 directly and will not invoke cb again
+  var cache = [];
+  var results = [];
+  var limitate = function(arg) {
+    var argIsThere = false;
+    var numindex = 0;
+    cache.forEach(function(num, i) {
+      if (arg === num) {
+        argIsThere = true;
+        numindex = i;
+      }
+    });
+    if (argIsThere) {
+      return results[numindex];
+    } else{
+      var result = cb(arg);
+      cache.push(arg);
+      results.push(result);
+      return result;
+    }
+  };
+  return limitate;
 }