2.5 KiB
Javascript Fundamentals Review
Primative Data Types
Javascript has several basic data types:
'this is a string' // string (text)
123 // number (int)
1.2 // number (float)
true // boolean
false // boolean
Variables
Declaring variables is done with the keyword var. Variables are dynamically typed (decided during execution) since there is no compilation process.
var foo = 'string';
var bar = 1;
Reassignment is done by omitting the var keyword. Variables are loosely typed (can be reassigned to any other value, regardless of their initial value)
var foo = 'a string';
foo = 123.4;
Functions and Scope
Declare functions with keyword function. Do not need to specify return type.
function myFunc(){
return 5;
}
To execute a function, invoke its name with parentheses
myFunc();
Can pass parameters into functions
function addFive(numberToAddFiveTo){
return numberToAddFiveTo + 5;
}
addFive(6); // returns 11
Variables declared inside a function cannot be accessed outside of it
function foo(){
var myVar = 1;
return myVar;
}
console.log(myVar); // error
but variables declared outside a function are accessible within it
var myVar = 1;
function foo(){
return myVar;
}
console.log(foo());
Objects
Objects in javascript are just key/value pairs
var myObj = {
property1: 'value1',
property2: 'value2'
}
Can retrieve values using dot notation
myObj.property1
Can modify an object's properties like so:
myObj.property1 = 'new value';
myObj.newProperty = 'asdf';
Arrays
Can create arrays, which are lists of elements of whatever type
var numbers = [1,'string',3.234,true];
Can access an array element by index (which start at 0)
numbers[0]; //first element in array
Can alter values at a preexisting index. Type does not matter
numbers[1] = 123;
Arrays are objects, so they have properties
numbers.length //gives you the length of the array
numbers.pop() //remove the last element and returns it
numbers.push(26) //adds a number to the last position of the array
numbers.shift() //remove the first element and returns it
numbers.unshift(56) //adds a number to the first position of the array and pushes everything down