JavaScript Flashcards by Kuddi Panda

scripts

programs that accompany web pages.

Run in web browsers and make web pages more dynamic and powerful

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variables

should start with lower case letter

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displays in browser console

console.log()

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displays on the web page

document.write()

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mark the end of a statement

semicolon

optional unless we write multiple statements in a single line

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comments

// single line
/*multi
line*/

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open the console

Ctrl + Shift + J

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javascript

programming language of the web

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create a variable

var name/identifier = value;

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undefined

a value

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maximum number of decimal places JavaScript can handle

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to know what type of data a variable contains

console.log(typeof(variable’s name));

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data types

string
numbers
Boolean
object

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special kind of comparison operator that requires the value and the type to be equal

===

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logical and

logical or

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assign a value to a variable based on a condition being true or false

conditional operator

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if non-boolean values have real value except 0, “”, undefined

when converted condition returns true

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perform different actions based on different condition

conditional statements

if, switch

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concatenate strings

string.concat(string);

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to find how many characters a string have

string.length;

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escaping character

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extract a piece of string

slice(start, end);

substr(start, length);

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replace

string.replace(search string, replace string);

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change a string to use lower/upper case letters

string. toLowerCase();

string. toUpperCase():

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multiplication and devision with a non-numeric string result in

NaN not a number but its type is number

casting

parstInt(string); | parseFloat(string);

round a number

Math.round(number);

Math.random();

produces a random number between 0 and 1

Date

date.getFullYear(); date.getMonth(); date.getDate(); date.getDay(); returns week day as a number from 0 to 6 toDateString();

special kind of variable that contains several values of a type or even different types

array great way to store related values var array_name = [content];

[ ]

array litteral

turns an array into a comma-separated string

array. toString(); | array. join();

a property that keeps track of number of values in the array

length

create arrays from strings

string.split(separator);

add values at the end of an array

array.push(value);

removes the last value from array

array.pop();

remove a value from the beginning of an array

array.shift();

add a value at the beginning of an array

array.unshift(value); | can use with multiple values

a method that can add, insert, replace and remove values

array.splice(index, how many values we want to remove, optional value to be added at the index);

sort an array

in alphabetical order - array.sort(); | reverse order - array.sort().reverse();

for loop

for(control_variable; condition; increment){statement;}

enhanced for loop

suppose thing is an array | for (var thing in things){......}

do while loop

runs at least one, even if the condition is false

skip specific iteration but continue loop

continue

find if a word ends with something

string.endsWith("text");

sample function definition

function sayHello(){console.log("Hello!");}

variables that contain several values or properties

objects

object literal

{ }

sample object

var person = {name:"Kajan", age:22, height:1.62};

if we want to get rid of a property

delete object.key;

defining a method

speak : function(){.........}

use ........... keyword to create as many instances of the object as we want

new

javascript can be placed in the ............. and the ............. sections of an HTML page

body | head

javascript display possibilites

writing into an alert box writing into an HTML output writing into an HTML element writing into the browser console

writing into an alert box

window.alert()

writing into an HTML output

document.write()

writing into an HTML element

using innerHTML

writing into the browser console

console.log()

javascript increases the speed by

validating user inputs before sending to the server and also reducing the load on the server

JavaScript code is written inside ............ of the html file you need to set the ............ attribute of the script to ...............

script tag type "text/javascript"

variables in javascript are declared using ........ keyword

var

in Javascript it is not required to specify the type of value a variable is going to hold

javascript itself takes care of it

variable name should start with

alphabet or underscore | cannot begin with numbers

javascript variables are .................

case sensitive

scope of javascript variable can be ............. or .............

local | global

a website might be just static content

web app would have dynamic content

the way javascript sees its containing pages' data

DOM - Document Object Model

render

to draw

display a message box with an OK button

alert()

display a message box which prompts for some user input

prompt(text, default_text)

display a dialog box with a message, ok and cancel button

confirm() | returns true if the user clicked ok

return true if the value and type of two variables are not equal

!==

conditional or ternary operators

checks a condition and based on the condition evaluates the value of a variable ?

bitwise and(&)

perform boolean AND operation on each bit of its variable

bitwise or

bitwise xor

bitwise not

left shift(<>)

to shift all bits in the first operand to left by the number of bits in the right operand

check whether a particular property is present within an object

in operator

check whether an object is an instance of the specified object

instanceof