reading-notes

Programming with JavaScript

MDN Control Flow

JavaScript Functions

JavaScript Operators

Expressions & Operators - Web Docs

Functions - Web Docs

Control Flow

• Control flow is the order in which the computer executes statements in a script
• Code is run in order from the first line to the last line, unless the computer encounters a code structure that changes the flow, such as conditionals or loops
  • In the example below, if the user leaves the field empty, they will be prompted to enter the data; otherwise, the form will be submitted

if(isEmpty(field)) {
  promptUser();
} else {
  submitForm();
}

JavaScript Functions

• Function is a block of code designed to perform a specific task
• A JS function is executed with something invokes it (calls it)
  • When an event occurs
  • When it is called from JavaScript code
  • Automatically, if self-invoked

Why Functions?

• Functions allow you to reuse code
  • Define the code once, and use it many times

JS Function Syntax

• Defined with the function keyword, followed by a name, followed by parentheses ()
• Code to be executed is contained within {}
• Parameters names are separated with commas ,

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

Function Return

• When JS reaches a return statement, the function will stop executing
• If the function was invoked from a statement, JS will “return” to execute the code after the invoking statement
• Functions often compute a return value that is then “return” 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 wil be:

12

Global vs. Local Variables

Global Variables

• Are declared outside of a function and are accessible to the entire code block

let carName = "Ford"
// code here CAN use carName

function myFunction() {
  return "I love my " + carName
// code here CAN use carName
}
// code here CAN use carName

Local Variables

• Are declared within a code block and are only accessible by that piece of code

// code here can NOT use carName

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

// code here can NOT use carName