ReadingNote201

JS-Basics

Statements should end with a semicolon. Each of the lines of code in green is a statement The pink curly braces indicate the start and end of a code block. (Each code block could contain many more statements.)

• JAVASCRIPT IS CASE SENSITIVE
• The semicolon also tells the JavaScript interpreter when a step is over, indicating that it should move to the next step.
• Some statements are surrounded by curly braces; these are known as code blocks.

  comments

  to explain what your code does for single line of comment // your comment for multiple line of comment /* your comment */

  variable

  A variable is a good name for this concept because the data stored in a variable can change

to dclear a variable var x ; and then you can assign value x=20 datatypes :

• NUMERIC DATA TYPE x= 7.5
• STRING DATA TYPE x = ‘string ‘
• BOOLEAN DATA TYPE (true or false) x = false

you can use scpe character to use the character that you cant use it (/) x= ‘dosen/’t’

• RULES FOR NAMING VARIABLES :
  • The name must begin with a letter, dollar sign ($),or an underscore (_).
  • The name can contain letters,numbers, dollar sign ($), or an underscore (_).
  • You cannot use keywords or reserved words.
  • All variables are case sensitive,
  • Use a name that describes the kind of information that the variable stores.
  • If your variable name is made up of more than one word, use a camelCase

    array :An array is a special type of variable. it stores a list of values

    to declear array :

  • var x; x=[‘element1’,’element2’,’element3’,…]
  • array constructor: var colors =new Array(‘white ‘ ,’black’,’custom ‘ );
• Each item in an array is automatically given a number called an index.start from 0
• ACCESSING ITEMS IN AN ARRAY :x[2]; to acces the element that has index number 2
• length holds the number of items in the array
• you can change the value of elemnt inside the array using this technique : x[2] = ‘new value’;
• An expression evaluates into (results in) a single value. Broadly speaking there are two types of expressions

  operators

• ASSIGNMENT OPERATORS Assign a value to a variable color = ‘beige’;
• COMPARISON OPERATORS <,>,==, !=,====,
• ARITHMETIC OPERATORS (+ - * /)

Decission and loops

decision

decision-making statement which is used to decide whether a block of JavaScript code will execute if a certain condition is true

• its defined which line of code should be run next

• A flowchart is a type of diagram that represents a workflow or process

• there are two component of decission :
  • expression
  • condition statment say what to do

• expression is to us comparission statment using (== ,!= ,=== ,!=== ,< ,> ,>= ,<=

• COMPARING TWO EXPRESSIONS : ex: var comparison= (score!+ score2) > (highScorel + highScore2);

logical operator

• operators that compare values and return true or false logical operators like :

  • or (

    ) its return false if both condition is false else it return true

  • and (&&) its return true if both condition is true else it return false
  • not (!) its return the opposite

    Conditional Statements:

    if

  • if to specify a block of code to be executed, if a specified condition is true
  • else to specify a block of code to be executed, if the same condition is false
  • else if to specify a new condition to test, if the first condition is false

    syntax

    if (condition) { // block of code to be executed if the condition is true } or if you have multiple cases if (condition1) { // block of code to be executed if condition1 is true } else if (condition2) { // block of code to be executed if the condition1 is false and condition2 is true } else { // block of code to be executed if the condition1 is false and condition2 is false }

    SWITCH STATEMENTS

    A switch statement starts with a variable called the switch value. Each case indicates a possible value for this variable and the code that should run if the variable matches that value.

    syntax

    switch(expression) { case x: // code block break; case y: // code block break; default: // code block }

DATA TYPE PURPOSE

string => Text number => Number Boolean => true or false null => Empty value undefined => Variable has been declared but not yet assigned a value

type coercion : JavaScript can convert data types behind the scenes to complete an operation strong typing :specify what data type each variable will be.

• JavaScript is said to use weak typing because the data type for a value can change. **unary operator ** returns a result with just one operand.

loops

if you want to run the same code over and over again, each time with a different value.

• there are three common types of loop:
  • for if you need to run the code specific number of time syntax: for (initial state; condition; incrementor decrement) { // code block to be executed }
  • while if you dont know how many times you need to run the code syntax : while (condition) { // code block to be executed }
  • do while same as while but the difference it that will run the statement inside barces at least one time even if the condition is false syntax: do { // code block to be executed } while (condition);

KEY LOOP CONCEPTS:

break:This keyword causes the termination of the loop and tells the interpreter to go onto the next statement of code outside of the loop. continue: This keyword te lls the interpreter to continue with the current iteration, and then check the condition again.