IES: JS-deck 12

Question 1

JS Asterisk

Answer 1

• the arithmetical multiplication operator in JavaScript

Question 2

JS Function Block

Answer 2

• can include a Return statement
• Common for statements in a function block to include calls to functions outside that function block

Question 3

JS Return Statement

Answer 3

• Can be included in / omitted from a JS function block
• without a value specified, function will return “undefined”
• Causes script flow to continue at caller
• No further function statements get executed
• Typical to pass manipulated argument values result to caller
  Ex.
  function function-name ( parameter, parameter ) {
  // Statements to be executed go here.
  return result
  }

Question 4

JS Invoke

Answer 4

• definition: called to execute their statements whenever required
• A usefulness of JS “functions”
• Entering different arguments, a caller can effect different results

Question 5

JS Parentheses

Answer 5

• JS operator
• Component of the call statement
• What actually calls the function
• A statement can assign a function to a variable by specifying just the function name (i.e. without the ( ) operator).
• A function name followed by ( ) will invoke the function and will return the assigned function value

Question 6

JS Interpreter

Answer 6

• reads scripts in top-to-bottom order
• Makes two sweeps
  1. First Sweep:
• Looks for function declarations
• remembers any found in a process known as “hoisting”
  2. Second sweep:
• the script is executed

Question 7

JS Hoisting

Answer 7

• the process whereby the interpreter appears to move the declaration of functions, variables, classes, or imports to the top of their scope, prior to execution of the code
• Occurs in the first sweep of the JS interpreter
• The JS interpreter looks for and remembers function declarations
• Allows function calls to appear in the script before the function declaration
• (the first sweep does not recognize functions using “let” or “const” keywords to assign variables)

Question 8

JS self-invoking function expressions

Answer 8

• a.k.a. IFFE (often pronounced- “iffy”)
• IFFE: Immediately Invoked Function Expressions
• Anonymous function expressions can be made “self-invoking” by enclosing entire function in ( ) and adding the ( ) operator at the end of the expression
  syntax:
  (function ( ) {statements; return value}) ( )
• This means that their statements are automatically executed one time when the script is first loaded by the browser

Question 9

JS anonymous functions

Answer 9

• a function name can be omitted when assigning a function to a variable
• This omission is possible because the function can be called in a statement specifying the variable name and the ( ) operator
• When assigning a named function to a variable, only specify the function name in the statement
  syntax:
  let variable = function (parameters) {statements; return value}
• Can be made “self-invoking” by enclosing entire function in ( ) and adding the ( ) operator at the end of the expression
  syntax:
  (function ( ) {statements; return value} ) ( )

Question 10

JS “lexical scope”

Answer 10

• the environment in which the variable was created
• Can be either “Global” or “local”
• Determines the extent to which variables are accessible in their scripts

Question 11

JS “global scope”

Answer 11

• A lexical scope
• refers to variables created outside function blocks
• Accessible globally during entire script (exists continuously and is available to functions within same script environment)
• can cause conflicts: can allow for variables of the same name but with different values to exist in the same environment
• Conflict potential is best avoided by never creating global variables which store primitive values

Question 12

JS “primitive values”

Answer 12

• all data types except “object” and “function”

Question 13

JS “local scope”

Answer 13

• a lexical scope
• variables created inside function blocks (Good practice: declare variables at the very beginning of a function block)
• Accessible locally throughout the function life (exists until function ends or until it returns)
• Recommended: try to create only local variables to store values within your scripts (avoids conflicts: like-named variables can exist within separate, included functions in the same script)

Question 14

JS store-value keywords

Answer 14

• “var”: allows like-named conflicting variables to overwrite their assigned values without warning
  1. And older keyword
• “let” and “const”:
  1. More recent keywords
  2. Prohibit overwriting their assigned values without warning
  3. recognize like-named conflicting variables as an “Uncaught SyntaxError”
• Recommended: create variables declared using the “let” or “const” keywords to store values within your scripts