array.md

Arrays

Arrays in JavaScript are ordered lists. They use integer indexes which can be accessed using bracket notation.

Arrays are mutable, meaning its state can be altered after it is created.

Iterating over arrays

forEach() iterates over an array, calling a callback function on every element. There is no "natural" way to break out of a forEach() loop; it will just keep going until the transversal is complete.

It takes three arguments: the element's value, the element's index, and the array.

const somelist = [1, 2, 3, 4, 5]

somelist.forEach((x, i, arr) => {
  console.log(`${x} is at position ${i} in ${arr}`)
})

for ... in is a conventional way for iterating over an array. Being a for loop, it can be broken out of using break and iterations can be skipped using continue.

for (let i = 0; i = somelist.length; i++) {
  console.log(`${somelist[i]} is at position ${i} in ${somelist}`)
}

Adding, removing elements

push(): add element to end of array

unshift(): add element to beginning of array

pop(): remove element from end of array; return that element

shift(): remove element from beginning of array; return that element

splice(index, deleteCount, ...elements): deletes deleteCount number of elements at index index and inserts elements at there

somelist.splice(1, 3, "a", "b", "c")  // → [ 1, 'a', 'b', 'c', 5 ]

Searching arrays

includes(element): returns true if array includes element

Copying arrays

slice(start[, end]): make a copy of an array starting from position start and ending at the optional position end – but not including the element at position end