Javascript Cheatsheet

#Comments Any to the right of // in Javascript is a comment and will be ignored by the computer. We use them to make notes and help other programmers understand what is happening.

// this is a comment
// so is this! var x = 1 never gets run

#Values There are different types of values you can use in Javascript. The main types are:

• Number (1, -214, 3.14159)
• String ("hello", "", "this is a string with symbols (!@)!@#}{")
• Boolean (true, false)

Numbers

A number is exactly what you would expect. You can do regular math with numbers in Javascript.

1 + 1
 => 2

4 - 3
 => 1

2 * 2
 => 4

12 / 4
 => 3

// % is called modulus - it tells you the remainder after division
// for example 11/5 = 2 remainder 1
11 % 5
 => 1

Strings

A string is any text surrounded by quotes. You can perform simple operations on strings:

"a string".length
 => 8

//substring gives you a piece of a string.
//the first number is the starting position
//and the second is the ending position + 1
//remember that the positions start at 0!
//here's a couple examples:
var s = "another string";

s.substring(0, 3);
 => "ano"
s.substring(2, 3);
 => "o"
s.substring(6, 6);
 => ""
s.substring(0, s.length);
 => "another string"

//you can also add strings and other values together with +
var s = "Hello ";
var name = "Bob";
console.log(s + name + 1);
 => Hello Bob1

Booleans

A boolean is value that can be either true or false. You can use the words true and false directly, or you can compare other values and get a boolean as the result. You can also combine booleans using the or and and operators.

1 > 3
 => false

//to compare for equality, use the '===' operator
12.3 === 12.3
 => true

//to compare for inequality, use the '!=' operator
16 != 42
 => true

"foo".length < 5
 => true

//&& means "and". If both boolean values are true, the result is true.
"foo".length < 5 && "foo" != "bad string"
 => true
"foobar".length < 5 && "foobar" != "bad string"
 => false

//|| means "or". If either boolean value is true, the result is true.
"foobar".length < 5 || "foobar" != "bad string"
 => true
"bad string".length < 5 || "bad string" != "bad string"
 => false

#Output console.log will print out the value or variable that you give it.

console.log(1);
 => 1

console.log("asdf");
 => asdf

console.log(false);
 => false

#Variables ##Declaring a variable The first time you want to use a variable, you must declare it with var and give it a name and value.

var x = 1;
var y = "baz";
var somethingelse = true;

##Using a variable Once a variable is declared, you can use it anywhere you would use a value.

var x = 1;
console.log(x);
 => 1

var x2 = x + 1;
console.log(x2);
 => 2

var y = "this is a string";
console.log(y);
 => this is a string

##Modifying a variable You can also change the value of a variable after it has been set.

var x = "foo";
console.log(x);
 => foo

x = "buh this isn't foo anymore";
console.log(x);
 => buh this isn't foo anymore

#If Statements An if statement lets you run different code depending on the condition. The condition must be any value or expression which results in a boolean value.

if (true) {
  console.log("the condition is true");
} else {
  console.log("the condition is false");
}
 => the condition is true

//you can use any comparison for the condition
var x = 12;
if (x < 6) {
  console.log("the condition is true");
} else {
  console.log("the condition is false");
}
 => the condition is false

//you can also only have an if case
var y = "foobar";
if (y.length < 12) {
  console.log("the condition is true");
}
 => the condition is true

var y = "foobar";
if (y.length > 12) {
  console.log("the condition is true");
}
 => <Nothing happens>

Functions

TBD