reading-notes

Read: 07 - Programming with JavaScript

MDN Control Flow

The order in which the computer executes statements in a script: Control Flow

• Code runs in orer from the first line in the file to the last line
  • Unless there are structures that change the control flow
    • These could be conditionals or loops
• Example of conditional structure such as if...else
• 
  • if...else executes different code depending on the input provided
• Typical JavaScript includes many control structures
  • conditionals, loops, and functions
  • may also be set to execute when specific events occur
• Control Structures can dictate complex flows of processing even with only a few lines of code
• Control Flow means that when you read a script you must not only read from start to finish but also look at program structure and how it affects the order of execution

JavaScript Functions (JS F)

• A JS F is a block of code designed to perform a particular task
• executed when “something” invokes (calls) it
• function myFunction(p1, p2){return p1 * p2;}

JS F Syntax

• JS F is defined with the function keyword, followed by a name, followed by ()

• F names can contain letters, digits, underscores, and dollar signs _{same rules as variables}

• () may include parameter names separated by commas
  • `(para1, para2, para3,…)
• The code to be executed by the function is placed within {}
• function name(para1, para2, para3){**code to be executed**}
• Function arguments are the values received by the function when invoked
• Inside the function, the arguments (the parameter) behave as local variables

Function Invocation

• Code inside function executes when “something” invokes (calls) the function:
  • event occurs (user clicks a button)
  • invoked (called) from JS code
  • Auto (self invoked)

Function Returns

• ex let x = myFunction(4, 3)
• ex function myFunction(a, b) {return a * b;} returns product of a*b as x

Why Functions?

• Reuse code! define it once and use it many times
• function toCel(fahrenheit) {return (5/9) * (fahrenheit-32);} document.getElementById("demo").innerHTML = toCel(77);
• toCel refers to the function object
• toCel() refers to the function result

• accessing a funtino without () returns the function object instead of the function result

• Functions can be used the same way as variables, in all types of formulas, assignments, and calculations.
• ex using a variable to store the return value of a function
  • let x = toCel(77); let text = "The temp is " + x + " Celsius";
• ex use the function directly, as a variable value
  • let text = "The temp is " + toCel(77) + " Celsius";
• Local Variables are variables declared within a JS F
  • They become LOCAL to the function
  • Can only be accessed from within the function
• ex function myFunction() {let carName = "Subaru"; code here CAN use carName} while any code outside of that function can NOT use carName
• However, you can use the same name for variables outside of the function or in different functions
• can be created when the function starts, and deleted when the function is complete

JS Operators (JS O)

• Assignment Operator
  • = assigns a value to a variable
  • ex let x = 10; assigns a value of 10 to variable x
  • + adds numbers
  • * multiplication operator
• biary operator ex: operand1 operator operand2
• unary operator ex: operator operand OR operand operator

Types of Operators

• Arithmetic perform arithmetic
• Assignment assign values to JS variables
• Comparison greater than, less tahn, equal to, not equal to
• String comparison operators used on strings; strings are compared alphabetically

• Logical *&& logical and;

  logical or; ! logical not*

• Bitwise work on 32 bit numbers; any numeric operand in the operation is converted into a 32 bit number. Result is converted back to a JS number
• Ternary
• Type returns variable type or returns true if an object is an instance of an object type; typeof or instanceof