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 = 'Link';
```

Escape Sequences in Strings

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

image.png

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

 
   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";
}

JavaScript基础

Introduction to JavaScript

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