Array
Methods
sort - sorts the items of array. By default, the sort method sorts the values as strings in alphabetical and ascending order.
var letters = ['D', "B", "A", "C"];
// Array [ "A", "B", "C", "D" ]
console.log(letters.sort());
// Numbers
var nums = [2, 3, 1, 6, 5, 4];
// Array [ 1, 2, 3, 4, 5, 6 ]
console.log(nums.sort(function(a, b){return a-b}))
Array.push() - adds an item to the end of the array so the return value is not the added item but instead is the new length of the array.
Array.unshift() - which adds an item to the beginning of the array, does the same thing: It returns the new array length.
Array.pop() - removes an item from the end of the array, but instead of returning the new array length, it returns the removed item.
Array.shift() - removes an item from the beginning of the array and, you guessed it, returns the removed item.
Iteration methods
Perform a load or wizardry while processing an array. All examples can be found as live code on this codepen.
All of the examples use the following demo array....
var arrPeople = [
{
'name': 'Shane',
'age': 29
},
{
'name': 'James',
'age': 35
},
{
'name': 'Ro',
'age': 28
},
{
'name': 'Jordan',
'age': 21
},
{
'name': 'Luc',
'age': 18
}
]
ES6 Syntax
arr.forEach((item) => {
console.log(item);
});
map - returns an array based on the arguments that you provide inside the map
// Map
var ages = arrPeople.map(function(obj) {
return obj.age;
});
foreach - loop through all of the array elements
// forEach
arrPeople.forEach(function(obj) {
//console.log(obj.name)
});
every - returns a boolean - true if every element in this array satisfies the provided testing function
// every
arrPeople.every(function(obj) {
return obj.age < 25;
});
some - returns a boolean - returns true if the callback function returns true for any array element; otherwise, false.
// some
arrPeople.some(function(obj) {
console.log(obj);
return obj.name === 'Shaney';
});
filter - returns an array based on the arguments that were true when looping
// Filter
var filtered = arrPeople.filter(function(obj) {
return obj.age < 30;
});
reduce - returns a value, takes the prev/next item int he array and can do what want with them in function, useful for summing the contents of array
// Reduce
arrPeople.reduce(function(a, b) {
if(a.age < b.age) return a
else return b
});
reduceRight - as above but starts at end goes backwards
// Reduce right
arrPeople.reduceRight(function(a, b) {
return b * a;
});
setTimeout inside an array method
fades.forEach((item, index) => {
setTimeout(function(){
whatever(item);
}, 1000 * index);
});
flat() - creates a new array with all sub-array elements concatenated into it recursively up to the specified depth.
const arr = [1, 2, [3, 4]];
arr.flat();
// [1, 2, 3, 4]
var arr2 = [1, 2, [3, 4, [5, 6]]];
arr2.flat(2);
// [1, 2, 3, 4, 5, 6]
flatMap() - like map, but flattens the result into a new array. Works the same as map followed by flat().
// [[29],[35],[28],[21],[18]];
arrPeople.map(x => [x.age * 2]);
// [29, 35, 28, 21, 18]
arrPeople.flatMap(x => [x]);
Chaining
// ES6
const combinedLegalAges = arrPeople
.filter(person => person.age > 17)
.map(legalPerson => legalPerson.age)
.reduce((a, b) => a + b);
const combinedLegalAges = arrPeople
.filter(function (person) {
return person.age > 17;
})
.map(function (legalPerson) {
return legalPerson.age;
})
.reduce(function (a, b) {
return a + b;
});
console.log(combinedLegalAges);
Array.prototype.fill()
const a = Array(10).fill(null);
var arr = [1, 2, 3, 4];
// fill with 0 from position 2 until position 4
console.log(arr.fill(0, 2, 4));
// expected output: [1, 2, 0, 0]
// fill with 5 from position 1
console.log(arr.fill(5, 1));
// expected output: [1, 5, 5, 5]
console.log(arr.fill(6));
// expected output: [6, 6, 6, 6]
Remove duplicate values from JS array
In ES6 you have Sets and Spread which makes it very easy and performant to remove all duplicates:
const b = [1,2,3,4,5,6,7,1,2,3,4,5,5]
console.log([ ...new Set(b) ]);
// [1, 2, 3, 4, 5, 6, 7]
Object within array
var uniq = a.reduce(function(a,b){
if (a.indexOf(b.country) < 0 ) a.push(b.country);
return a;
},[]);
Find duplicates in Array
var names = ['Mike', 'Matt', 'Nancy', 'Adam', 'Jenny', 'Nancy', 'Carl']
var uniq = names
.map((name) => {
return {
count: 1,
name: name
}
})
.reduce((a, b) => {
a[b.name] = (a[b.name] || 0) + b.count
return a
}, {})
var duplicates = Object.keys(uniq).filter((a) => uniq[a] > 1)
console.log(duplicates) // [ 'Nancy' ]
Array destructuring
const a = [1,2,3];
const [one, two, three] = a;
// 1
console.log(one)
StackOverflow by Christian Landgren