JavaScript基础

JavaScript基础这一部分算是非常入门级的内容，包括JS的基本变量类型以及相应的基本操作。这一部分就不做过多的总结了，习题解答如下：

Introduction to JavaScript

• Comment Your JavaScript Code

  //This is a single-line comment
  /* This is a 
      multiline comment */

• Declare JavaScript Variables

  var myName;

• Storing Values with the Assignment Operator

  a = 7;
  b = a; 

• Initializing Variables with the Assignment Operator

  var a = 9;

• Understanding Uninitialized Variables

  var a = 5;
  var b = 10;
  var c = "I am a";

• Understanding Case Sensitivity in Variables

  // Declarations
  var studlyCapVar;
  var properCamelCase;
  var titleCaseOver;
  
  // Assignments
  studlyCapVar = 10;
  properCamelCase = "A String";
  titleCaseOver = 9000;

• Add Two Numbers with JavaScript

  var sum = 10 + 10;

• Subtract One Number from Another with JavaScript

  var difference = 45 - 33;

• Multiply Two Numbers with JavaScript

  var product = 8 * 10;

• Divide One Number by Another with JavaScript

  var quotient = 66 / 33;

• Increment a Number with JavaScript

  myVar++;

• Decrement a Number with JavaScript

  myVar--;

• Create Decimal Numbers with JavaScript

  var myDecimal = 3.2;

• Multiply Two Decimals with JavaScript

  var product = 2.0 * 2.5;

• Divide One Decimal by Another with JavaScript

  var quotient = 4.4 / 2.0; 

• Finding a Remainder in JavaScript

  var remainder = 11 % 3;

• Compound Assignment With Augmented Addition

  a += 12;
  b += 9;
  c += 7;

• Compound Assignment With Augmented Subtraction

  a -= 6;
  b -= 15;
  c -= 1;

• Compound Assignment With Augmented Multiplication

  a *= 5;
  b *= 3;
  c *= 10;

• Compound Assignment With Augmented Division

  a /= 12;
  b /= 4;
  c /= 11;

• Declare String Variables

  var myFirstName = "Nikkkki";
  var myLastName = "Xu";

• Escaping Literal Quotes in Strings

  var myStr = "I am a \"double quoted\" string inside \"double quotes\"."; 

• Quoting Strings with Single Quotes

  var myStr = '<a href="http://www.example.com" target="_blank">Link</a>';

• Escape Sequences in Strings

  var myStr = "FirstLine\n\t\\SecondLine\nThirdLine";

  

• Concatenating Strings with Plus Operator

  var myStr = "This is the start. " + "This is the end.";

• Concatenating Strings with the Plus Equals Operator

  var myStr = "This is the first sentence. ";
  myStr += "This is the second sentence.";

• Constructing Strings with Variables

  var myName = "Nikkkki";
  var myStr = "My name is " + myName + " and I am well!";

• Appending Variables to Strings

  var someAdjective = "interesting";
  var myStr = "Learning to code is ";
  myStr += someAdjective;

• Find the Length of a String

  lastNameLength = lastName.length;

• Use Bracket Notation to Find the First Character in a String

  firstLetterOfLastName = lastName[0];

• Understand String Immutability

  myStr = "Hello World";

• Use Bracket Notation to Find the Nth Character in a String

  var thirdLetterOfLastName = lastName[2];

• Use Bracket Notation to Find the Last Character in a String

  var lastLetterOfLastName = lastName[lastName.length - 1];

• Use Bracket Notation to Find the Nth-to-Last Character in a String

  var secondToLastLetterOfLastName = lastName[lastName.length-2];

• Word Blanks

  function wordBlanks(myNoun, myAdjective, myVerb, myAdverb) {
    // Your code below this line
    var result = "";
      result = myNoun + " " + myAdjective + " " + myVerb + " " + myAdverb;
    // Your code above this line
    return result;
  }

• Store Multiple Values in one Variable using JavaScript Arrays

  var myArray = ["kitty", 5];

• Nest one Array within Another Array

  var myArray = [["dog", 5], ["cat", 3]];

• Access Array Data with Indexes

  var myData = myArray[0];

• Modify Array Data With Indexes

  myArray[0] = 45;

• Access Multi-Dimensional Arrays With Indexes

  var myData = myArray[2][1];

• Manipulate Arrays With push()

  myArray.push(["dog", 3]);

• Manipulate Arrays With pop()

  var removedFromMyArray = myArray.pop();

• Manipulate Arrays With shift()

  var removedFromMyArray = myArray.shift();

• Manipulate Arrays With unshift()

  myArray.unshift(["Paul", 35]);

• Shopping List

  var myList = [["milk", 4], ["biscuits", 22], ["chocolate", 6], ["honey", 2], ["ice cream", 9]];

• Write Reusable JavaScript with Functions

  function reusableFunction() {
      console.log("Hi World");
  }
  reusableFunction();

• Passing Values to Functions with Arguments

  function functionWithArgs(param1, param2) {
    console.log(param1 + param2);
  }
  functionWithArgs(3, 2);

• Global Scope and Functions

  // Declare your variable here
  var myGlobal = 10;
  
  function fun1() {
    // Assign 5 to oopsGlobal Here
    oopsGlobal = 5;
  }
  
  // Only change code above this line
  function fun2() {
    var output = "";
    if (typeof myGlobal != "undefined") {
      output += "myGlobal: " + myGlobal;
    }
    if (typeof oopsGlobal != "undefined") {
      output += " oopsGlobal: " + oopsGlobal;
    }
    console.log(output);
  }

• Local Scope and Functions

  function myLocalScope() {
    'use strict'; // you shouldn't need to edit this line
    var myVar = "hello";
    console.log(myVar);
  }
  myLocalScope();
  
  // Run and check the console
  // myVar is not defined outside of myLocalScope
  // console.log(myVar);

• Global vs. Local Scope in Functions

  function myOutfit() {
    // Only change code below this line
    var outerWear = "sweater";
    // Only change code above this line
    return outerWear;
  }

• Return a Value from a Function with Return

  function timesFive(num) {
    return num * 5;
  }
  console.log(timesFive(2));

• Understanding Undefined Value returned from a Function

  function addFive() {
    sum = sum + 5;
  }

• Assignment with a Returned Value

  processed = processArg(7);

• Stand in Line

  function nextInLine(arr, item) {
    // Your code here
    arr.push(item);
    var result = arr.shift();
    return result;  // Change this line
  }

• Understanding Boolean Values

  function welcomeToBooleans() {
    // Only change code below this line.
  
    return true; // Change this line
  
    // Only change code above this line.
  }

• Use Conditional Logic with If Statements

  function trueOrFalse(wasThatTrue) {
    // Only change code below this line.
    if(wasThatTrue) {
        return "Yes, that was true"
    }
    return "No, that was false"; 
    // Only change code above this line.
  }

• Comparison with the Equality Operator

  function testEqual(val) {
    if (val == 12) { // Change this line
      return "Equal";
    }
    return "Not Equal";
  }

• Comparison with the Strict Equality Operator

  function compareEquality(a, b) {
    if (a === b) { // Change this line
      return "Equal";
    }
    return "Not Equal";
  }

• Practice comparing different values

  function testNotEqual(val) {
    if (val!=99) { // Change this line
      return "Not Equal";
    }
    return "Equal";
  }

• Comparison with the Inequality Operator

  function testStrictNotEqual(val) {
    // Only Change Code Below this Line
    if (val !== 17) {
    // Only Change Code Above this Line
      return "Not Equal";
    }
    return "Equal";
  }

• Comparison with the Strict Inequality Operator

  function testGreaterThan(val) {
    if (val > 100) {  // Change this line
      return "Over 100";
    }
    if (val > 10) {  // Change this line
      return "Over 10";
    }
    return "10 or Under";
  }

• Comparison with the Greater Than Operator

  function testGreaterOrEqual(val) {
    if (val >= 20) {  // Change this line
      return "20 or Over";
    }
    if (val >= 10) {  // Change this line
      return "10 or Over";
    }
    return "Less than 10";
  }

• Comparison with the Greater Than Or Equal To Operator

  function testLessThan(val) {
    if (val < 25) {  // Change this line
      return "Under 25";
    }
    if (val < 55) {  // Change this line
      return "Under 55";
    }
    return "55 or Over";
  }

• Comparison with the Less Than Operator

  function testLessOrEqual(val) {
    if (val <= 12) {  // Change this line
      return "Smaller Than or Equal to 12";
    }
    if (val <= 24) {  // Change this line
      return "Smaller Than or Equal to 24";
    }
    return "More Than 24";
  }

• Comparison with the Less Than Or Equal To Operator

  function testLogicalAnd(val) {
    // Only change code below this line
    if (val <= 50 && val >= 25) {
      return "Yes";
    }
    // Only change code above this line
    return "No";
  }

• Comparisons with the Logical And Operator

  function testLogicalOr(val) {
    // Only change code below this line
    if (val > 20 || val < 10) {
      return "Outside";
    }
    // Only change code above this line
    return "Inside";
  }

• Comparisons with the Logical Or Operator

  function testElse(val) {
    var result = "";
    // Only change code below this line
    if (val > 5) {
      result = "Bigger than 5";
    }else {
      result = "5 or Smaller";
    }
    // Only change code above this line
    return result;
  }

• Introducing Else Statements

  function testElseIf(val) {
    if (val > 10) {
      return "Greater than 10";
    } else if (val < 5) {
      return "Smaller than 5";
    } else {
      return "Between 5 and 10";
    }
  }

• Logical Order in If Else Statements

  function orderMyLogic(val) {
    if (val < 5) {
      return "Less than 5";
    } else if (val < 10) {
      return "Less than 10";
    } else {
      return "Greater than or equal to 10";
    }
  }

• Chaining If Else Statements

  function testSize(num) {
    // Only change code below this line
    if(num < 5) {
      return "Tiny";
    } else if (num < 10) {
      return "Small";
    } else if (num < 15) {
      return "Medium";
    } else if (num < 20) {
      return "Large";
    } else {
      return "Huge";
    }
    // Only change code above this line
  }

• Golf Code

  function golfScore(par, strokes) {
    // Only change code below this line
    if(strokes === 1) {
      return names[0];
    } else if (strokes <= par - 2) {
      return names[1];
    } else if (strokes === par - 1) {
      return names[2];
    } else if (strokes === par) {
      return names[3];
    } else if (strokes === par + 1) {
      return names[4];
    } else if (strokes === par + 2) {
      return names[5];
    } else {
      return names[6];
    }
    // Only change code above this line
  }

• Selecting from Many Options with Switch Statements

  function caseInSwitch(val) {
    var answer = "";
    // Only change code below this line
    switch(val) {
      case 1:
        answer = "alpha";
        break;
      case 2:
        answer = "beta";
        break;
      case 3:
        answer = "gamma";
        break;
      case 4:
        answer = "delta";
        break;
    }
    // Only change code above this line  
    return answer;  
  }

• Adding a Default Option in Switch Statements

  function switchOfStuff(val) {
    var answer = "";
    // Only change code below this line
    switch(val) {
      case "a":
        answer = "apple";
        break;
      case "b":
        answer = "bird";
        break;
      case "c":
        answer = "cat";
        break;
      default:
        answer = "stuff";
        break;
    }
    // Only change code above this line  
    return answer;  
  }

• Multiple Identical Options in Switch Statements

  function sequentialSizes(val) {
    var answer = "";
    // Only change code below this line
    switch(val) {
      case 1:
      case 2:
      case 3:
        answer = "Low";
        break;
      case 4:
      case 5:
      case 6:
        answer = "Mid";
        break;
      case 7:
      case 8:
      case 9:
        answer = "High";
        break;
    }
    // Only change code above this line  
    return answer;  
  }

• Replacing If Else Chains with Switch

  function chainToSwitch(val) {
    var answer = "";
    // Only change code below this line
    switch(val) {
      case "bob":
        answer = "Marley";
        break;
      case 42:
        answer = "The Answer";
        break;
      case 1:
        answer = "There is no #1";
        break;
      case 99:
        answer = "Missed me by this much!";
        break;
      case 7:
        answer = "Ate Nine";
        break;
    }
    // Only change code above this line  
    return answer;  
  }

• Returning Boolean Values from Functions

  function isLess(a, b) {
    // Fix this code
      return a < b;
  }

• Return Early Pattern for Functions

  function abTest(a, b) {
    // Only change code below this line
    if(a < 0 || b < 0) {
      return undefined;
    }
    // Only change code above this line
    return Math.round(Math.pow(Math.sqrt(a) + Math.sqrt(b), 2));
  }

• Counting Cards

  function cc(card) {
    // Only change code below this line
    switch(card) {
      case 2:
      case 3:
      case 4:
      case 5:
      case 6:
        count += 1;
        break;
      case 10:
      case 'J':
      case 'Q':
      case 'K':
      case 'A':
        count -= 1;
        break;
    }
    var str ='';
    if(count > 0) {
      str = "Bet";
    } else {
      str = "Hold";
    } 
    return count + " " + str;
    // Only change code above this line
  }

• Build JavaScript Objects

  var myDog = {
    "name" : "Stone",
    "legs": 4,
    "tails": 1,
    "friends": ["Pepe"]
  };

• Accessing Object Properties with Dot Notation

  var hatValue = testObj.hat;      // Change this line
  var shirtValue = testObj.shirt;    // Change this line

• Accessing Object Properties with Bracket Notation

  var entreeValue = testObj["an entree"];   // Change this line
  var drinkValue = testObj["the drink"];    // Change this line

• Accessing Object Properties with Variables

  var playerNumber = 16;       // Change this Line
  var player = testObj[playerNumber];   // Change this Line

• Updating Object Properties

  myDog.name = "Happy Coder";

• Add New Properties to a JavaScript Object

  myDog.bark = "woof";

• Delete Properties from a JavaScript Object

  delete myDog.tails;

• Using Objects for Lookups

  function phoneticLookup(val) {
    var result = "";
    // Only change code below this line
    var lookup = {
      "alpha": "Adams",
      "bravo": "Boston",
      "charlie": "Chicago",
      "delta": "Denver",
      "echo": "Easy",
      "foxtrot": "Frank"
    }
    result = lookup[val];
    // Only change code above this line
    return result;
  }

• Testing Objects for Properties

  function checkObj(checkProp) {
    // Your Code Here
    if(myObj.hasOwnProperty(checkProp)) {
      return myObj[checkProp];
    }
    return "Not Found";
  }

• Manipulating Complex Objects

  var myMusic = [
    {
      "artist": "Billy Joel",
      "title": "Piano Man",
      "release_year": 1973,
      "formats": [ 
        "CD",
        "8T",
        "LP"
      ],
      "gold": true
    },
    // Add record here
    {
      "artist": "Alicia Keys",
      "title": "If I ain't got you",
      "release_year": 2000,
      "formats": [
        "CD",
        "LP"
      ]
    }
  ];

• Accessing Nested Objects

  var gloveBoxContents = myStorage.car.inside["glove box"];

• Accessing Nested Arrays

  var secondTree = myPlants[1].list[1];

• Record Collection

  function updateRecords(id, prop, value) {
    if(prop !== "tracks" && value !== "") {
      collection[id][prop] = value;
    } else if(prop === "tracks" && !collection[id].hasOwnProperty("tracks")) {
      collection[id].tracks = [];
      collection[id].tracks.push(value);
    } else if (prop === "tracks" && value !== "") {
      collection[id].tracks.push(value);
    } else if (value === "") {
      delete collection[id][prop];
    }
    return collection;
  }

• Iterate with JavaScript While Loops

  var i = 0;
  while(i < 5) {
    myArray.push(i);
    i ++;
  }

• Iterate with JavaScript For Loops

  for(var i = 1; i < 6; i ++) {
      myArray.push(i);
  }

• Iterate Odd Numbers With a For Loop

  for(var i = 1; i < 10; i += 2) {
    myArray.push(i);
  }

• Count Backwards With a For Loop

  for(var i = 9; i > 0; i -= 2) {
    myArray.push(i);
  }

• Iterate Through an Array with a For Loop

  var total = 0;
  for(var i = 0; i < myArr.length; i ++) {
    total += myArr[i];
  }

• Nesting For Loops

  function multiplyAll(arr) {
    var product = 1;
    // Only change code below this line
    for(var i = 0; i < arr.length; i ++) {
      for(var j = 0; j <arr[i].length; j ++) {
        product *= arr[i][j];
      }
    }
    // Only change code above this line
    return product;
  }

• Iterate with JavaScript Do…While Loops

  do {
    myArray.push(i);
    i++
  } while(i<5);

• Profile Lookup

  function lookUpProfile(name, prop){
  // Only change code below this line
    for(var i = 0; i < contacts.length; i ++) {
      if(contacts[i].firstName === name) {
        if(contacts[i].hasOwnProperty(prop)) {
          return contacts[i][prop];
        } else {
          return "No such property";
        }
      } 
    }
    return "No such contact";
  // Only change code above this line
  }

• Generate Random Fractions with JavaScript

  function randomFraction() {
    // Only change code below this line.
    return Math.random();
    // Only change code above this line.
  }

• Generate Random Whole Numbers with JavaScript

  function randomWholeNum() {
    // Only change code below this line.
    return Math.floor(Math.random()*10);
  }

• Generate Random Whole Numbers within a Range

  function randomRange(myMin, myMax) {
    return Math.floor(Math.random()*(myMax-myMin+1)) + myMin; // Change this line
  }

• Use the parseInt Function

  function convertToInteger(str) {
    return parseInt(str);
  }

• Use the parseInt Function with a Radix

  function convertToInteger(str) {
    return parseInt(str, 2);
  }

• Use the Conditional (Ternary) Operator

  function checkEqual(a, b) {
    return a === b ? true : false;
  }

• Use Multiple Conditional (Ternary) Operators

  function checkSign(num) {
    return num > 0 ? "positive" : (num === 0) ? "zero" : "negative";
  }