- Basic JavaScript Knowledge
- Variables
- Data types- there are 8 JS data types.
- 1. String: a series of characters, written with single or double quotes
- 2. Number: can be integers or decimals.
- 3. Bigint: used to store integer values that are too big to be represented by a normal JS number
- 4. Boolean: true or false, used in conditional testing
- 5. Undefined: a variable without a value, has the value undefined/empty values
- 6. Null: represents the intentional absence of any object value
- 7. Symbol: used to represent unique values that can be used as identifiers/keys in objects.
- 8. Object: an unordered collection of key-value pairs. Each key-value pair is called a property.
- Const
- Conditionals: control behavior, decides whether or not pieces of code can run.
- Functions:
- Iteration:
- JavaScript in HTML- Questions
- Hacks
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 mySymbol = Symbol();
const myObject = {
[mySymbol]: 'Hello World'
};
console.log(myObject[mySymbol]);
Edit/add to the code above so that it outputs "Hello World"
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
let today = new Date();
let currentHour = today.getHours();
if (currentHour < 12) {
console.log("Good morning!");
} else if (currentHour < 18) {
console.log("Good afternoon!");
} else {
console.log("Good evening!");
}
Create a conditional statement about how you would greet someone based on the time of day.
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 the JavaScript code in the <head> of an HTML page.
- How do you import a JS file into HTML?
Use .js and < script > tag
- What is onClick?
onClick is when user clicks on something and it triggers
- What tag do you use to write JavaScript code?
The < script > tag