Basic JavaScript Knowledge
var x = 5;
var y = 6;
var z = x + y;
z
let text = "Mort";
text
let text2 = 'Yeung';
text2
let number = 1234567890123456789012345n;
let Largenum = BigInt(1234567890123456789012345)
let typeLargenum = typeof Largenum;
typeLargenum
Largenum
Boolean(10 > 9)
Write a boolean statement that outputs true
let name;
name
grade = undefined;
let result;
result = Boolean(undefined);
console.log(result); // false
result = Boolean(null);
console.log(result); // false
7. Symbol: used to represent unique values that can be used as identifiers/keys in objects.
- They are also used to create private properties and methods in classes.
- unique and immutable, so they can be used as unique identifiers in objects and classes.
- useful for creating constants that can be shared across different parts of your code.
// Create a Symbol
const mySymbol = Symbol();
console.log(mySymbol);
// expected output: Symbol()
const myObject = {
[mySymbol]: 'Hello World'
};
console.log(myObject);
Edit/add to the code above so that it outputs "Hello World"
const myObjects = {
[mySymbol]: 'Hello World'
};
console.log(myObjects[mySymbol]);
Object
- Identify the name/keys in the object below: name, breed, age, color
- Identify the values in the object below: Elly, Rottweiler, 4, black
const dogs = {name: "Elly", breed:"Rottweiler", age:4, color:"black"}
dogs
Array
const songs = ["Love Story", "Blank Space", "I Knew You Were Trouble"];
songs
const cost1 = 2;
const cost2 = 11;
let totalCost = cost1 + cost2;
totalCost
Conditionals: control behavior, decides whether or not pieces of code can run.
- If: if a condition is true it is used to specify execution for a block of code.
- Else: if the same condition is false it specifies the execution for a block of code.
- Else If: new test if the first condition is false.
if (10 > 5) {
var outcome = "True";
}
outcome;
if ("red" === "blue") {
var outcome = "if block";
} else {
var outcome = "else block";
}
outcome;
let temperature = 54
if (temperature < 70) {
cast = "Chilly";
} else if (temperature < 60) {
cast = "Cold";
} else {
cast = "Warm";
}
cast
Create a conditional statement about how you would greet someone based on the time of day. let timeOfDay = "evening";
if (timeOfDay == "morning") { greeting = "Good Morning"; } else if (timeOfDay == "afternoon") { greeting = "Good Afternoon"; } else if (timeOfDay == "evening") { greeting = "Good Evening"; }
greeting
Iteration:
- for loop: repeats until a specified condition evaluates to false
- do...while: repeats until a specified condition evaluates to false
- while statement: executes its statements as long as a specified condition evaluates to true
- label: provides a statement with an identifier that lets you refer to it later in the code. ex. you can use a label to identify a loop, and then use the break or continue statements to indicate whether a program should interrupt the loop or continue its execution
- break: used to terminate a loop, switch, or in conjunction with a labeled statement
- continue: can be used to restart a while, do-while, for, or label statement
- for...in: iterates a specified variable over all the enumerable properties of an object
- for...of statement creates a loop Iterating over iterable objects, invoking a custom iteration hook with statements to be executed for the value of each distinct property
JavaScript in HTML- Questions
- Where do you store the JavaScript Code? You store it within a script tag in html allowing to acsess to javascript code.
- How do you import a JS file into HTML? Imports are with an src as seen imbeded in a script tag for ex script src="path/to/my-script.js"> script
- What is onClick? Onclick is a function that gives a response such as an answer a color change when a button is clicked.
- What tag do you use to write JavaScript code? You use the script tag for javascript code.
<!DOCTYPE html>
<html>
<head>
<title>Quiz</title>
</head>
<body>
<h1>Quiz</h1>
<h2>Question 1:</h2>
<p>What is the first letter in the alphabet</p>
<input type="text" id="answer1">
<br><br>
<h2>Question 2:</h2>
<p>what it messi first name</p>
<input type="text" id="answer2">
<br><br>
<button onclick="checkAnswers()">Submit</button>
<script>
function checkAnswers() {
const answer1 = document.getElementById("answer1").value;
const answer2 = document.getElementById("answer2").value;
let score = 0;
if (answer1.toLowerCase() === "a") {
score++;
}
if (answer2.toLowerCase() === "lionel") {
score++;
}
alert(`You scored ${score} out of 2.`);
}
</script>
</body>
</html>