Intro Flashcards
In JavaScript, the console keyword refers to . . .
an object, a collection of data and actions, that we can use in our code. Keywords are words that are built into the JavaScript language, so the computer recognizes them and treats them specially.
One action, or method, that is built into the console object is the .log() method.
When we write console.log() what we put inside the parentheses will get printed, or logged, to the console.
how would you type console.log?
console.log( );
As we write JavaScript, we can write comments in our code that the computer will ignore as our program runs. These comments exist just for human readers.
Comments can explain what the code is doing, leave instructions for developers using the code, or add any other useful annotations.
A single line comment will comment out a single line and is denoted with two forward slashes // preceding it.
e.g. //this prints 20 to the console
A multi-line comment will comment out multiple lines and is denoted with /* to begin the comment, and */ to end the comment.
e.g. /* this is an example*/
What are data types?
Data types are the classifications we give to the different kinds of data that we use in programming. In JavaScript, there are eight fundamental data types:
Data type numbers
Number: Any number, including numbers with decimals: 4, 8, 1516, 23.42.
Data type Bigint
BigInt: Any number, greater than 253-1 or less than -(253-1), with n appended to the number: 1234567890123456n.
Data type string
String: Any grouping of characters on your keyboard (letters, numbers, spaces, symbols, etc.) surrounded by single quotes: ‘ … ‘ or double quotes “ … “, though we prefer single quotes. Some people like to think of string as a fancy word for text.
Data type boolean
Boolean: This data type only has two possible values— either true or false (without quotes). It’s helpful to think of booleans as on and off switches or as the answers to a “yes” or “no” question.
Data type null
Null: This data type represents the intentional absence of a value, and is represented by the keyword null (without quotes).
Data type undefined
Undefined: This data type is denoted by the keyword undefined (without quotes). It also represents the absence of a value though it has a different use than null. undefined means that a given value does not exist.
Data type symbols
Symbol: A newer feature to the language, symbols are unique identifiers, useful in more complex coding. No need to worry about these for now.
Data type object
Object: Collections of related data.
JavaScript has several built-in arithmetic operators, that allow us to perform mathematical calculations on numbers.
These include the following operators and their corresponding symbols:
Add: +
Subtract: -
Multiply: *
Divide: /
Remainder: %
e.g.
console.log(3 + 4); // Prints 7
console.log(5 - 1); // Prints 4
console.log(4 * 2); // Prints 8
console.log(9 / 3); // Prints 3
Note that when we console.log() the computer will evaluate the expression inside the parentheses and print that result to the console.
If we wanted to print the characters 3 + 4, we would wrap them in quotes and print them as a string.
Note that when we console.log() the computer will evaluate the expression inside the parentheses and print that result to the console.
If we wanted to print the characters 3 + 4, we would wrap them in quotes and print them as a string.
The remainder operator %
The remainder operator, sometimes called modulo, returns the number that remains after the right-hand number divides into the left-hand number as many times as it evenly can: 11 % 3 equals 2 because 3 fits into 11 three times, leaving 2 as the remainder.
Operators aren’t just for numbers! When a + operator is used on two strings, it appends the right string to the left string:
console.log(‘hi’ + ‘ya’); // Prints ‘hiya’
console.log(‘wo’ + ‘ah’); // Prints ‘woah’
console.log(‘I love to ‘ + ‘code.’)
// Prints ‘I love to code.’
All data types have access to specific properties that are passed down to each instance. For example, every string instance has a property called length that stores the number of characters in that string.
The . is another operator! We call it the dot operator.
console.log(‘Hello’.length); // Prints 5
In the example above, the value saved to the length property is retrieved from the instance of the string, ‘Hello’. The program prints 5 to the console, because Hello has five characters in it.
Remember that methods are actions we can perform. Data types have access to specific methods that allow us to handle instances of that data type. JavaScript provides a number of string methods.
We call, or use, these methods by appending an instance with:
a period (the dot operator)
the name of the method
opening and closing parentheses
E.g. ‘example string’.methodName().
You can find a list of built-in string methods in the JavaScript documentation. Developers use documentation as a reference tool. It describes JavaScript’s keywords, methods, and syntax.
Does that syntax look a little familiar? When we use console.log() we’re calling the .log() method on the console object. Let’s see console.log() and some real string methods in action!
console.log(‘hello’.toUpperCase()); // Prints ‘HELLO’
console.log(‘Hey’.startsWith(‘H’)); // Prints true
On the first line, the .toUpperCase() method is called on the string instance ‘hello’. The result is logged to the console. This method returns a string in all capital letters: ‘HELLO’.
In addition to console, there are other objects built into JavaScript. Down the line, you’ll build your own objects, but for now these “built-in” objects are full of useful functionality.
console.log(Math.random()); // Prints a random number between 0 and 1
For example, if you wanted to perform more complex mathematical operations than arithmetic, JavaScript has the built-in Math object.
The great thing about objects is that they have methods! Let’s call the .random() method from the built-in Math object:
To generate a random number between 0 and 50, we could multiply this result by 50, like so:
Math.random() * 50;
he example above will likely evaluate to a decimal. To ensure the answer is a whole number, we can take advantage of another useful Math method called Math.floor().
Math.floor() takes a decimal number, and rounds down to the nearest whole number. You can use Math.floor() to round down a random number like this:
Math.floor(Math.random() * 50);
Math.random() generates a random number between 0 and 1.
We then multiply that number by 50, so now we have a number between 0 and 50.
Then, Math.floor() rounds the number down to the nearest whole number.
console.log(Math.floor(Math.random() * 50)); // Prints a random whole number between 0 and 50
