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Js notes.md

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Javascript notes-

5 Primitive Datatypes-

  • Numbers
  • Strings
  • Booleans
  • null
  • undefined

built-in methods-

  • alert()
  • prompt()
  • console.log()
  • clear()

While Loops-

Repeat code WHILE a condition is true

while(someCondition) {
  //run some code
}

For Loops-

for(init; condition; step) {
  //run some code
}

Arrays-

We can initialize an empty array two ways:

var friends = []; //no friends :(
var friends = new Array() //uncommon

Arrays can hold any type of data

var random_collection = [49, true, "Hermione", null];

Arrays have a length property

var nums = [45,37,89,24];
nums.length   //4

Strings-

Single or Double quotes OK

"hello world"
'hello world'

Concatenation

"charlie" + "brown"  //"charliebrown"

Escape Characters start with ""

"Singin \"Do wah diddy, diddy, dum diddy do\" "
"This is a backslash: \\"

Strings have a length property

"hello world".length  //11

Access individual characters using [] and an index

"hello"[0]  //"h"
"hello"[4]  //"o"

Array methods-

  • push/pop
  • unshift/shift
  • indexOf
  • slice
arr.slice(startIndex,endIndex)

you can also use slice() to copy an entire array

var otherNums = arr.slice();

Array Iteration-

for(var i = 0; i < colors.length; i++) {
  console.log(colors[i]);
}

or

arr.forEach(function(color){
//color is a placeholder, call it whatever you want
  console.log(color);
});

Functions-

Functions let us wrap bits of code up into REUSABLE packages. They are one of the building blocks of JS.

function doSomething() {
  console.log("HELLO WORLD");
}

Objects-

var person = {
  name: "Cindy", 
  age: 32,
  city: "Missoula",
  addToAge:function(x){return x+this.age;}
};

bracket notation, similar to arrays:

person["name"];

dot notation:

person.name;
person.addToAge(1); // returns 33

UNDERSCORE

http://underscorejs.org/

Dom Methods-

document.getElementById()  //return match

document.getElementsByClassName() //returns array

document.getElementsByTagName()  //returns array

document.querySelector()  //returns first match

document.querySelectorAll()  //returns array

ADD A CLASS TO THE SELECTED ELEMENT

tag.classList.add("another-class");

REMOVE A CLASS

tag.classList.remove("another-class");

TOGGLE A CLASS

tag.classList.toggle("another-class");

Retrieve the textContent:

tag.textContent();

Attributes

Use getAttribute() and setAttribute() to read and write attributes like src or href

var link = document.querySelector("a")
link.getAttribute("href");
link.setAttribute("href","www.google.com");

Event Listener-

element.addEventListener(type,functionToCall);

Mdn events list-

https://developer.mozilla.org/en-US/docs/Web/Events