These are my notes while doing the course JavaScript Algorithms and Data Structures on https://www.freecodecamp.org. I highly recommend it if you prefer to try things directly rather than watching videos.
Note: In JavaScript arrays are technically a type of object. Therefore arrays are also capable of storing complex objects.
/* Modify Array Data with Indexes */ var myArray = [50,40,30]; myArray[0] = 15; // equals [15,40,30] /* Access Multi-Dimensional Arrays with Indexes */ var myArray = [ [1,2,3], [4,5,6], [7,8,9], [[10,11,12], 13, 14] ]; myArray[3]; // equals [[10,11,12], 13, 14] myArray[3][0]; // equals [10,11,12] myArray[3][0][1]; // equals 11 /* Manipulate Arrays with push() -> adding to the end */ var myArray = [1,2,3]; myArray.push(4); // myArray is now [1,2,3,4] /* Manipulate Arrays with pop() -> removing last element */ var threeArr = [1, 4, 6]; var oneDown = threeArr.pop(); console.log(oneDown); // Returns 6 console.log(threeArr); // Returns [1, 4] /* Manipulate Arrays with shift() -> removing first element */ var myArray = ["Stimpson", "J", ["cat"]]; var removedFromOurArray = myArray.shift(); console.log(removedFromOurArray); // Returns "Stimpson" console.log(myArray); // Returns ["J", ["cat"]] /* Manipulate Arrays with unshift() -> adding to the beginning */ var myArray = ["Stimpson", "J", "cat"]; myArray.shift(); // myArray now equals ["J", "cat"] myArray.unshift("Happy"); // myArray now equals ["Happy", "J", "cat"] /* Manipulate Arrays with concat() -> append i.e. another array. */ var firstArray = [1, 2, 3]; var secondArray = [4, 5, 6]; var thirdArray = firstArray.concat(secondArray); // thirdArray now equals [ 1, 2, 3, 4, 5, 6 ] /* Also useable to clone an array (will do a copy by reference!) */ var fourthArray = [].concat(firstArray); // FourthArray now equals [1, 2, 3] /* Remove & Add Items using splice() -> remove any number of consecutive elements from anywhere in an array. */ /* First parameter: index */ /* Second parameter: number of elements to delete */ let array = ['today', 'was', 'not', 'so', 'great']; array.splice(2, 2); // array now equals ['today', 'was', 'great'] /* Third parameter: add elements to the array. Useful for quickly switching out an element, or a set of elements, for another. */ const numbers = [10, 11, 12, 12, 15]; numbers.splice(3, 1, 13, 14); // returns [ 10, 11, 12, 13, 14, 15 ] /* Copy Array Items Using slice() -> copies or extracts a given number of elements to a new array, leaving the array it is called upon untouched */ let weatherConditions = ['rain', 'snow', 'sleet', 'hail', 'clear']; let todaysWeather = weatherConditions.slice(1, 3); // todaysWeather equals ['snow', 'sleet']; /* Copy an Array with the Spread Operator -> allows to easily copy all of an array's elements. Syntax: ... */ let thisArray = [true, true, undefined, false, null]; let thatArray = [...thisArray]; // thatArray equals [true, true, undefined, false, null] /* Combine Arrays with the Spread Operator */ let fragment = ['to', 'code']; let sentence = ['learning', ...fragment, 'is', 'fun']; // sentence equals ['learning', 'to', 'code', 'is', 'fun'] /* Check For The Presence of an Element With indexOf() -> takes element as parameter. Returns the position (index) or -1 if element does not exist */ let fruits = ['apples', 'pears', 'oranges', 'peaches', 'pears']; fruits.indexOf('dates'); // returns -1 fruits.indexOf('oranges'); // returns 2 fruits.indexOf('pears'); // returns 1, the first index at which the element exists /* The reduce() method reduces the array to a single value. It executes a provided function for each value of the array (from left-to-right).*/ /* First parameter: The initialValue, or the previously returned value of the function */ /* Second parameter: The value of the current element */ /* 0 is set as initialValue */ const args = [2, 4, 2]; const sum = args.reduce((a, b) => a + b, 0); // returns 8
And there are several other build in methods to iterate over arrays like every(), forEach(), map(), etc.
https://www.w3schools.com/jsref/jsref_obj_array.asp