reading-notes

Class 7 - Programming with JavaScript

Control Flow

• control flow - The order in which the computer executes statements in a script. Code is run in order from the first line in the file to the last line, unless the computer runs across the structures that change the control flow, such as conditionals, loops, and functions.

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Functions

• function - a block of code designed to perform a particular task and is executed when “something” invokes it (calls it)

function myFunction(p1, p2) {
  return p1 * p2;   // The function returns the product of p1 and p2
}

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Function Syntax

• a JavaScript function is defined with the function keyword, followed by a name, followed by parentheses: ()
• function names can contain letters, digits, underscores, and dollar signs (same rules as variables)
• the parentheses may include parameter names separated by commas: (parameter1, parameter2, ...)
• the code to be executed by the function is placed inside curly brackets: {}
• function arguments (parameters) are the values received by the function when it is invoked, which behave as local variables

function name(parameter1, parameter2, parameter3) {
  // code to be executed
}

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Function Return

• when JavaScript reaches a return statement, the function will stop executing
• if the function was invoked from a statement, JavaScript will “return” to execute the code after the invoking statement
• Functions often compute a return value. The return value is “returned” back to the “caller”:

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 x will be 12

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Invoking (Calling) a Function

• the code inside the function will execute when “something” invokes (calls) the function:
  • when an event occurs (when a user clicks a button)
  • when it is invoked (called) from JavaScript code
  • automatically (self invoked)
• accessing a function without () will return the function object instead of the function result

function toCelsius(fahrenheit) {
  return (5/9) * (fahrenheit-32);
}
document.getElementById("demo").innerHTML = toCelsius;

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Variables

Using a Function as a Variable

• functions can be used the same way as you use variables, in all types of formulas, assignments, and calculations

let text = "The temperature is " + toCelsius(77) + " Celsius";

Local Variables

• variables declared within a JavaScript function, become LOCAL to the function
• local variables can only be accessed from within the function

// code here can NOT use carName

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

// code here can NOT use carName

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Why Functions?

• you can reuse code: Define the code once, and use it many times
• you can use the same code many times with different arguments, to produce different results

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JavaScript Operators

• the assignment operator = assigns a value to a variable:

let x = 10;

• the addition operator + adds numbers:

let x = 5;
let y = 2;
let z = x + y;

• the multiplication operator * multiplies numbers:

let x = 5;
let y = 2;
let z = x * y;

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Types of JavaScript Operators

There are different types of JavaScript operators:

• Arithmetic Operators
• Assignment Operators
• Comparison Operators
• Logical Operators
• Conditional Operators
• Type Operators

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Arithmetic Operators

+      Addition
-      Subtraction
*      Multiplication
**     Exponentiation (ES2016)
/       Division
%       Modulus (Division Remainder)
++     Increment
--     Decrement

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Assignment Operators

Operator     Example     Same As
=               x = y               x = y
+=               x += y               x = x + y
-=               x -= y               x = x - y
*=               x *= y               x = x * y
/=               x /= y               x = x / y
%=               x %= y               x = x % y
**=               x **= y               x = x ** y

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Comparison Operators

Operator     Description
==               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

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Logical Operators

Operator      Description
&&                 logical and
||                logical or
!                 logical not