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javascript-array.md

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Arrays

An array is a data structure that allows us to store a collection of values in a single variable.

Syntax

Defining an array:

const myArray = [1, 5, 10, 42];

Accessing array element(s)

myArray[0]; // returns 1
myArray[1]; // returns 5
myArray[2]; // returns 10
myArray[3]; // returns 42
myArray[4]; // returns undefined

Adding array element(s)

myArray.push(43);
// Note: this mutates the state of the original array. We will learn another way of doing this in the ES6 chapter that does not mutate the original array

Removing array elements

  • myArray.slice(i, [j])

    • i is the starting index

    • j (optional) is the ending index (non-inclusive of the element at index j). If excluded, the ending index is

    • this method does not mutate myArray. Rather, it returns a new array

      const animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];

animals.slice(2);  // returns ["camel", "duck", "elephant"]

animals.slice(2, 4); // returns ["camel", "duck"]

animals.slice(1, 5); // returns ["bison", "camel", "duck", "elephant"]

Joining arrays to form strings

// syntax: someArray.split(someDelimiter)

['hello', 'who', 'are', 'you'].join('_') // 'hello_who_are_you'
['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd'].join('') // returns 'hello world'

Creating arrays from strings using String.split()

// syntax: someString.split(someDelimiter)

'hello world'.split(' ') // returns ['hello', 'world']
'hello world'.split('') // returns ['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']

You can also create arrays from strings using Array.from()

Array.from('hello world') // returns ['h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd']

Resources

Lab