JavaScript
REPL - Read Evaluate Print Loop
JavaScript Arrays
Arrays are the ordered collection of values.
let students = []; //empty array
let colors = ['red', 'orange', 'yellow']; // string array
let numbers = [19,22,56,12,51]; // number array
let stuff = [true, 68, 'cat', null]; // mixed array
numbers.length // will give you the length
[].length // 0
colors[1][0] // o
Modifying Arrays
let colors = ['rad', 'orange', 'yellow'];
colors[0] = 'red' // rad -> red
colors[10] = 'indigo' // ['red', 'orange', 'yellow', emptyx7, 'indigo']
Array methods Push - add to the end Pop - remove from end Shift - remove from start Unshift - add to start concat - merge arrays includes - look for a value indexOf - just like string.indexOf join - create a string from an array reverse - reverse an array slice - copies a portion on an array splice - removes/replaces elements sort - sort an array
let movieLine = ['tom', 'nancy'];
movieLine.push('pablo') // adds pablo at the end
movieLine.push('eva', 'oliver')
movieLine.pop() // removes oliver
movieLine.shift() // removes and returns tom
movieLine.unshift('harry') // adds at the first index
let array1 = ['a', 'b', 'c'];
let array2 = ['d', 'e', 'f'];
let array3 = array1.concat(array2);
let beasts = ['ant', 'bison', 'camel', 'duck', 'bison'];
console.log(beasts.indexOf('bison')); // returns 1
let elements = ['Fire', 'Air', 'Water'];
console.log(elements.join());
// expected output: "Fire,Air,Water"
console.log(elements.join(''));
// expected output: "FireAirWater"
console.log(elements.join('-'));
// expected output: "Fire-Air-Water"
let array1 = ['one', 'two', 'three'];
console.log('array1:', array1);
// expected output: "array1:" Array ["one", "two", "three"]
let reversed = array1.reverse();
console.log('reversed:', reversed);
// expected output: "reversed:" Array ["three", "two", "one"]
// Careful: reverse is destructive -- it changes the original array.
console.log('array1:', array1);
// expected output: "array1:" Array ["three", "two", "one"]
let animals = ['ant', 'bison', 'camel', 'duck', 'elephant'];
console.log(animals.slice(2));
// expected output: Array ["camel", "duck", "elephant"]
console.log(animals.slice(2, 4));
// expected output: Array ["camel", "duck"]
console.log(animals.slice(1, 5));
// expected output: Array ["bison", "camel", "duck", "elephant"]
let months = ['Jan', 'March', 'April', 'June'];
months.splice(1, 0, 'Feb');
// inserts at index 1
console.log(months);
// expected output: Array ["Jan", "Feb", "March", "April", "June"]
let months = ['March', 'Jan', 'Feb', 'Dec'];
months.sort();
console.log(months);
// expected output: Array ["Dec", "Feb", "Jan", "March"]
let array1 = [1, 30, 4, 21, 100000];
array1.sort();
console.log(array1);
// expected output: Array [1, 100000, 21, 30, 4]
Reference Types and Equality Testing
['hi', 'bye'] === ['hi', 'bye'] // will return False
Javascript doesn’t compare contents of the array, it compares the references in the memory.
let nums = [1, 2, 3];
let numsCopy = nums;
nums === numsCopy // will return True as it is comparing the reference.
We can use const with an array, because while creating an array using const the variable name for example
const nums =[1,2,3,4] the reference of the nums is not changing, so we can change the values or contents of it. But as soon as we try to assign the variable into something totally different or to new reference it will show an error.