Arrays are used to store a collection of variables.
var list = ["A", "B", "C", "D"];
var list2 = [1, 10, 0, 3];
var list3 = [1, 'ten', '0', 3];
You can access individual items in an array by referencing its index or position. Accessing an invalid index will return
undefined.
Arrays operate off of a "zero" based index. The first position has an index of 0.
var list = ["A", "B", "C", "D"];
console.log(list[1]); // Outputs "B"
console.log(list[0]); // Outputs "A"
console.log(list[20]); // Outputs undefined
There are several different methods to modify an array. We're going to focus primarily on one.
push - Adds item to the end of an arraylength - gives the count of items in the array
var x = ["a", "b", "c"];
x.push('d');
x.push('e');
console.log(x); //["a", "b", "c", "d", "e"];
Just about everything in JavaScript is an object. Primitive variables are the only things that are not actual objects.
Objects are variables that contain many variables.
var person = {
firstName: "Jon",
lastName: "Middaugh",
age: 28,
city: 'Johnson',
fullName: function(){
// return this.firstName + " " + this.lastName;
var me = this;
return me.firstName + " " + me.lastName;
}
};
console.log(person.age) //Outputs 28;
console.log(person.height); //Outputs undefined
person.height = '5\' 6"';
console.log(person.height); //Outputs 5' 6"
this
var person = {
firstName: "Jon",
lastName "Middaugh",
age: 28,
city: 'Cave Springs',
fullName: function(){
return this.firstName + " " + this.lastName;
};
};
There is a very easy way to increment or decrementing a variable. You can use the ++ or -- to increment or decrement your variable by 1.
var x = 0;
x++ // equivalent to x = x + 1;
console.log(x); //outputs 1
x++
console.log(x); //outputs 2
x--
console.log(x); //outputs 1
Loops in JavaScript are used to execute the same statement multiple times.
The for loop is most often used when dealing with collections.
for (
statement 1;
statement 2;
statement 3;
){
//Code Block
}
var x = [1, 2, 3, 4];
for(var i = 0; i < x.length; i++){
console.log(x[i]);
}
var x = [1, 2, 3, 4];
var i = 0;
for(; i < x.length; i++){
console.log(x[i]);
}
var names = ['Jon', 'Benjamin', 'Kristin'];
var htmlString = "<ul>"
for( var i = 0; i < names.length; i++){
htmlString = htmlString + '<li>' + names[i] + '</li>'
}
htmlString = htmlString + '</ul>';
var names = [
{ firstname: 'John', lastname: 'Doe'},
{ firstname: 'Jane', lastname: 'Doe'}
];
var html = "<ul>"
for( var i = 0; i < names.length; i++){
html = html + '<li>' + names[i].firstname + ' ' + names[i].lastname + '</li>'
}
html = html + '</ul>';
var array = [1,2,3,4,5]
for(var i = array.length; i>0; i--){
}
Do and While loops are easier to read, but require more care to code properly.
May not execute depending on the condition.
var i = 0;
while(i < 25){
console.log('i is equal to ' + i);
i++
}
Will always execute at least once.
var i = 0;
do{
console.log('i is equal to ' + i);
i++
}
while (i < 25);
var condition = false;
var i = 0;
while(condition == false){
if (i > 10){
condition = true;
}
i++
}
Scope is the collection of variables, objects and functions you have the ability to access.
Local scope is a group of items that can only be accessed within the context it is declared.
function testing(){
var x = 0;
console.log(x); //logs 0
}
testing();
console.log(x); // Causes an error
Global scope items can be accessed by all JavaScript on the page.
var x = 0;
function testing(){
console.log(x); //logs 0
}
testing();
console.log(x); //logs 0;
Dates are variable types that represent a date and time inside of JavaScript.
Dates are stored as the number of milliseconds since January 1, 1970.
Example: 4/5/2017 is roughly - 1491415025702
Example : 1/1/1777 is roughly - -6090400800000
//Creates a date variable that is set to now;
var now = new Date(); // Wed Apr 05 2017 12:57:05 GMT-0500 (Central Daylight Time);
var newDate = new Date(1491415025702); //Tue Aug 17 2010 12:09:36 GMT-0500 (Central Daylight Time)
var newDate = new Date("2010/08/17 12:09:36");
//Fri Jan 01 2010 00:00:00 GMT-0600 (Central Standard Time)
var newDate2 = new Date("1/1/2010");
new Date(year, month[, date[, hours[, minutes[, seconds[, milliseconds]]]]]);
Note: Month is zero based.
//Tue Feb 01 2010 00:00:00 GMT-0600 (Central Standard Time)
var d = new Date(2010, 1)
//Thu Apr 15 2010 12:04:14 GMT-0500 (Central Daylight Time)
var d = new Date(2010, 3, 15, 12, 4, 14)
var d = new Date('9/9/2017')
var d = new Date(2017, 8, 9)
Dates have very long outputs by default, but there are methods to retrieve parts of a date.
var d = new Date(2010, 0, 1);
console.log(d.getFullYear()); //2010;
console.log(d.getDate()); // 1
var d = new Date(1993,6, 28);
console.log(d.toString()); // logs Wed Jul 28 1993 14:39:07 GMT-0600 (PDT)
console.log(d.toDateString()); // logs Wed Jul 28 1993
console.log(d.toTimeString()); // logs 14:39:07 GMT-0600 (PDT)
We use set methods change these values.
var d = new Date(2010, 0, 1);
d.setDate(7) // 1-7-2010;
d.setMonth(1) // 2-7-2010;
d.setHours(40); // 2-8-2010 16:00
console.log(d);
var d1 = new Date(1990, 1, 1);
var d2 = new Date(2000, 1, 1);
var isNewer = d2 > d1; //True
Let's get the current date and add a week to it.
var d1 = new Date();
var curDate = d1.getDate(); //Get the number for the current Date
var newDate = curDate + 7; //Add value to it
d1.setDate(newDate); // Set the new date
console.log(d1);
//Shorter
var d1 = new Date();
var newDate = d1.getDate() + 7;
d1.setDate(newDate);
console.log(d1);
//Even Shorter
var d1 = new Date();
d1.setDate(d1.getDate() + 7);
console.log(d1);
You don't have to stick to the traditional restrictions when adding values.
You have 90 days from today for a warranty.
You don't have to calculate the number of months. JS will automatically handle the overflow.
var d1 = new Date();
d1.setDate(d1.getDate() + 90);
console.log(d1);