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JavaScript is not Java
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Interactive elements like tabs, sliders, etc
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You can mix JavaScript and HTML. The script tag tells your browser the stuff inside is code, not content.
<script>
CODE GOES HERE
</script>
Just like CSS, you can split a long block of JavaScript into its own file.
<script src="path/to/file.js"></script>
gdi
.index.html
.<!DOCTYPE html>
<html>
<head>
<title>Test Page</title>
</head>
<body>
<p>This is my awesome JavaScript code.</p>
<script>
alert('Hello World!');
console.log('Secret message');
</script>
</body>
</html>
Computers are great at processing. They are bad at understanding.
When you write a program, you must break down every step into simple pieces.
Source: Harvard Students Making Sandwich: CS 50 Algorithm Intro
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You can see what's going on in the console.
Each instruction in JS is a "statement", like:
console.log('Hello World!');
console.log('I am glad to meet you');
console.log('I am fuzzy');
You can leave comments in your code—notes that people can read but computers will ignore.
/*
I can make long comments
with multiple lines here
*/
console.log('Hello World!'); // Or make short comments here
Open a popup box.
alert('Hello World!');
Display a message in your console.
console.log('Hello World!');
Add something to the page.
document.write('Hello World!');
index.html
.mycode.js
.Just like 'x' in algebra, a variable is a named container for a value that can change.
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To declare (create) a variable, just type the word var
and the variable name.
var numberOfKittens;
It is a good idea to give your variable a starting value. This is called initializing the variable.
var numberOfKittens = 5;
undefined
).$
, or _
.Once you have created a variable, you can use it in your code. Just type the name of the variable.
var numberOfKittens = 5;
console.log(numberOfKittens);
In your JavaScript file, create a variable and give it a valid name and value. Then, display the value.
var userName = 'Jane Lane';
var myAge = 30;
var catsAreBest = true;
var favoriteThings;
var goodPickupLines = null;
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Variables can be numbers, either integers or floats (decimals).
var numberOfKittens = 5;
var cutenessRating = 9.6;
JavaScript automatically converts integers to floats
NaN
= Not-A-Number
Once you have numbers, you can do math with them!
var numberOfKittens = 5;
var numberOfPuppies = 4;
var numberOfAnimals = numberOfKittens + numberOfPuppies;
Example | Name | Result |
---|---|---|
-a |
Negation | Opposite of a . |
a + b |
Addition | Sum of a and b . |
a - b |
Subtraction | Difference of a and b . |
a * b |
Multiplication | Product of a and b . |
a / b |
Division | Quotient of a and b . |
a % b |
Modulus | Remainder of a divided by b . |
Create two variables and try some arithmetic operators. Don't forget to display your results!
Variables can be strings (groups of characters). You put your string in single or double quotes.
var kittensName = 'Fluffy';
If you want to use a quote in your string, you'll need to escape it with a backslash.
console.log('I\'d like to use an apostrophe');
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You can put strings together with a +
, the concatenation operator.
var kittensName = 'Fluffy ';
var fullName = kittensName + 'McDougle';
console.log(fullName); // Outputs 'Fluffy McDougle'
You can also use +=
to add things to the end of a string.
var kittensName = 'Admiral ';
kittensName += 'Snuggles';
console.log(kittensName); // Outputs 'Admiral Snuggles'
Create two variables, a first name and a last name, and then put them together to make a full name. Don't forget to display your results!
You can use concatenation to mix strings and numbers. When you do this, JavaScript will treat the number like a string.
var numberOfFruit = 6;
var typeOfFruit = 'bananas';
var allTheFruit = 'I have ' + numberOfFruit + ' ' + typeOfFruit + '!';
console.log(allTheFruit);
Create a program to calculate the tip at a restaurant. It should:
toFixed()
to round the bill total to 2 decimals.