Loops - patrickcole/learning GitHub Wiki

Loops

For Loop

  • The traditional for loop.
  • We start with a initial state (ex: let i = 0)
  • Next, a conditional statement, that while still true will continue to execute the loop; if false, it will stop executing the loop
  • Finally, what happens at the end of each step of the loop (ex: i++ or "increase the value of i by 1)
const vaughnHello = ['hey','sup','greetings'];
for ( let i = 0; i < vaughnHello.length; i++ ) {
  console.log(vaughnHello[i]);
}

// => "hey"
// => "sup"
// => "greetings"

// "That guy always says hi three different ways"

for...in

Used for looping through items that are enumerables, or items that are "being counted one at a time. This means the collection's elements can be distinctly identified and referenced." (Mehraban, dev.to - Apr. 24, 2020)

const vehicle = {
  color: 'black',
  type: 'sedan',
  year: '2017',
  make: 'Honda',
  model: 'Civic LX'
}

for ( let key in vehicle ) {
  console.log(`${key}: ${vehicle[key]}`);
}

// => "color: black"
// => "type: sedan"
// => "year: 2017"
// => "make: Honda",
// => "model: Civic LX"

for...in can be used on other enums such as an Array or String. However, you cannot use for...in on Symbols.

for...of

Applies to iterable objects. Objects where an action is repeated on each item of the iterable.

const stock = [3,10,49];
for ( let amount of stock ) {
  console.log(`Amount of each item: ${amount}`);
}

// => "Amount of each item: 3"
// => "Amount of each item: 10"
// => "Amount of each item: 49"

Can also be used with String

const greeting = "Hello";
for ( let char of greeting ) {
  console.log(char);
}

// => "H"
// => "e"
// => "l"
// => "l"
// => "o"

Sources