Notes

Conditionals

Control Flow : The order in which instructions are executed within a program.

Control Structures : Expressions that alter the control flow based on given parameters.

Conditional Statements : A control structure that is used to perform different actions based on different conditions.

• [] : square brackets;
• {} : curly braces;
• () : parenthesis;

Writing Conditional Statements

• If Statements : The simplest type of conditional statement.
• Else If Statements : conditional statements chained after if statements to test additional statements.

• Else Statement : statement that will evaluate if prior conditions are deemed falsey.

  if (test expression {
      // execute this;
  })
  
  if (x === 3) {
      console.log("this is a three!");
  } else if (x === 4) {
      console.log("this is a four!");
  } else {
      console.log("this is neither a three nor four!");
  }

• There can be any amount of else if statements, however there will only be one if statement and one else statement.

• Think of them as a chain. > Fun Fact : Nesting the else/if and else chains are called ‘cuddled else’s’; this is common JS style but functionally they help the reader see more information in a more concise way.

• Guard Clauses : useful to refactor conditional logic and to reduce the number of lines in your functions.

  (before guard clause)
  if (true) {
    return x;
  } else {
    return y;
  }
  
  (after guard clause)
  if (true) return x;
  return y;

Mutually Exclusive Conditions

When to use If Statements

If we are working with a situation that is mutually exclusive, then we should use an If/Else Statement.

Age old principal for writing good code: DRY (Don’t repeat yourself)!

• Collectively Exhaustive : Set of events if at least one of those events must occur within a specific scenario. (Think of covering all edge cases)
• Edge Cases : problem or situation that occurs only at an extreme (maximum or minimum) operating parameter.

Basic Loops

Loops : Are a fundamental control structure that will repeatedly execute a section of code while a condition is true.

While Loops : Will execute a block of code as long a specified condition is true.

while (condition) {
  // code block to be executed
}

let index = 0;
while (index < 10) {
  console.log("The number is " + index);
  index++;
}

• The most important thing to remember when writing loops is to always be working towards your condition, if we omitted the index++ our loop would run infinitely; likely crashing w/e we were working on.

Important Loop Knowledge

• Don’t forget to always start your loops with a zero index.

• iteration : the act of repeating a procedure; looping is an iterative technique

For Loops For loops can be broken down into three sections:

• The initial expression
• The condition
• The loopEnd expression

for (<initital expression>;<condition>;<loopEnd expression>) {};

• For loops are usually used with an integer counter.

Translating From One Loop to Another

Here is an example of the same loop expressed as a while and for loop.

function forLoopDoubler (array) {
for (let i = 0; i < array.length; i++>) {
array[i] = array[i] \* 2
}
return array;
};

function forLoopDoubler (array) {
let i = 0;
while (i < array.length>) {
array[i] = array[i] \* 2;
i++;
}
return array;
};

Arrays

Using Arrays

• Arrays are very flexible data containers, we can input elements, replace elements, and also remove elements.
• .length property also works on arrays.
• Arrays that consist of multiple values are store in sequential order; arrays will always start at a zero index.

Working with Arrays

• Arrays can hold different types of data and can mix & match; however it is considered good practice to lump similar data types together if possible.
• indexOf() function can be used with arrays.
• If you concatenate two arrays with the + operator it will convert your combined arrays into strings.
• If you use the .concat method, it will combine two arrays into a single array.