reading-notes

Class 7 Notes

Control Flow

Source: https://developer.mozilla.org/en-US/docs/Glossary/Control_flow

• Control flow is the order in which the computer executes statements in a script, typically from the first line to the last line.
• Control structures like conditionals and loops can change control flow.
• Conditional structure is if…else
• Script can also be set to execute when events occur.
• Control flow means that when you read a script, you need to not only read from stat to finish, but look at program structure and how it affects order of execution.

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JS Functions

Source: https://www.w3schools.com/js/js_functions.asp

• A JS function is:
  1. a block of code designed to perform a specific task
  2. executed when “something” invokes it.

Example: ‘ // Function to compute the product of p1 and p2 function myFunction(p1, p2) { return p1 * p2; }’

Function Syntax

• A JS function is defined with the ‘function’ keyword, followed by a ‘name’, followed by parentheses ‘()’.
• function names can contain letters, digits, _ and $
• the parenthesis may include parameter names separated by commas: ex. (parameter1, parameter2,…)
• the code to be executed by the function is placed in curly brackets {}

Example: ‘ function name (parameter1, parameter2, parameter3) { // code to be executed }’

• Function parameters are listed inside the parentheses () in the function definition.
• Function arguments are the values received by the function when it’s invoked.
• When inside a function, arguments (parameters) act as local variables.

Function Invocation

• the code inside the function will execute when “something” invokes the function:
  1. when an event occurs (ex. user clicks button)
  2. When it’s invoked from JS code
  3. Automatically (i.e. self invoked)

Function Return

• When JS gets to a return statement, the function stops executing
• If the function was invoked from a statement, JS will “return” to execute the code after invoking the statement.
• Functions often compute a return value - which is “returned” back to the “caller.”

Example: ‘let x = myFunction (4, 3); // Function is called, return value will end up in x

function myFunction(a b) { return a * b; // Function returns the product of a and b }’

The result in this case is 12

Why Functions

1. It allows you to reuse code - define it once and use it many times
2. It allows you to use the same code many times with different arguments, and to produce different results

The () Operator Invokes the Function

• accessing a function without () will return the function object instead of the function result.

Example: ‘function toCelsius(fahrenheit) { return (5/9) * (fahrenheit-32); } document.getElementById(“demo”).innerHTML = toCelsius’

Functions Used As Variable Values

• Functions can be used the same was as variables, and in all types of formulas/assignments/calculations.

Example: Instead of using a variable to store the return value of a function: ‘let x = toCelsius(77); let text = “The temperature is “ + x + “ Celsius”;’

Use the function directly as a variable value: ‘let text = “The temperature is “ + toCelsius(77) + “ Celsius”;’

Local Variables

• Variables declared in a JS function become local to the function.
• Local variables can only be accessed from within the function.

Example: ‘ // code here can NOT use carName

function myFunction() { let carName = “Volvo”; // code here CAN use carName }

// code here can NOT use carName’

• Since local variables are only recognized inside their functions, variables with the same name can be used in different functions.
• Local variables are created when a function starts, and deleted when a function is completed.

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JS Operators

Source: https://www.w3schools.com/js/js_operators.asp

• Assignment Operator (=) assigns a value to a variable.

Example:

1. ‘let x = 10;’

• Addition Operator (+) adds numbers

Example: ‘let x = 5; let y = 2; let z = x + y;’

• Multiplication Operator (*) multiplies numbers

Example: ‘let x = 5; let y = 2; let z = x * y;’

Types of JS Operators

1. Arithmetic: perform arithmetic on numbers: ‘let a = 3; let x = (100 + 50) * a;’
2. Assignment: assign values to variables
   • Addition Assignment Operator (+=) adds value to a variable: ‘let x = 10; x += 5;’
   • The + operator AND the += operator can also be used to add (concatenate) strings.
   • When used on strings, the + operator is called the concatenation operator
   • Adding two numbers will return a sum but adding a number + string returns a string
3. Comparison:
   • Examples:

   • == equal to

     === equal value and equal type

     != not equal

     !== not equal value or not equal type

     > greater than

     < less than

     >= greater than or equal to

     <= less than or equal to

     ? ternary operator

4. Logical:
   • Examples:

   • && logical and

     logical or

     ! logical not

5. Conditional
6. Type:
   • Examples:

   • typeof returns the type of a variable

     instanceof returns true if an object is an instance of an object type

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Things I Want To Know More About

Nothing at this time.

URL: https://s-glass.github.io/reading-notes/102/class7notes