JS cheat sheet
Array manipulation methods​
Those examples was made from node REPL
> var doo = ['a', 'b', 'c']
undefined
Creating a simple array
Reverse​
> doo.reverse()
[ 'c', 'b', 'a' ]
Reverse method will just reverse our array
Slice​
> const arr = [1, 2, 3, 4, 5, 6, 7 ,8, 9, 10, 11]
undefined
> arr.slice(1,5)
[ 2, 3, 4, 5 ]
> arr.slice(3)
[
4, 5, 6, 7,
8, 9, 10, 11
]
Slice we are able to specify the beginning and the final where we want to cut from an array
> const arr = [1, 2, 3, 4, 5, 6, 7 ,8, 9, 10, 11]
> arr.slice(3, 8)
[ 4, 5, 6, 7, 8 ]
This example, as we can see, we specify that we going to cut all number under 4, and cut all number above 8
It is important to notice, the number is the index for each value
> const abc = ['a','b','c','d','e','f','g']
undefined
> abc.slice(3,5)
[ 'd', 'e' ]
ForEach​
> doo.forEach(s => console.log(s))
a
b
c
undefined
Creating a loop using the method forEach, but we also are able to do that using
map()
Using Map​
> doo.map(a => a)
[ 'a', 'b', 'c' ]
We are also able to do more things using map()
> doo.map(a => a + ' xss')
[ 'a xss', 'b xss', 'c xss' ]
We are able to concatenate string
Below we can see examples using map:
> var numr = [1, 2, 3, 4, 5]
undefined
> numr
[ 1, 2, 3, 4, 5 ]
> numr.map(a => a)
[ 1, 2, 3, 4, 5 ]
> numr.map(a => a+1)
[ 2, 3, 4, 5, 6 ]
> numr.map(a => a*2)
[ 2, 4, 6, 8, 10 ]
> numr.map(a => a+' pos')
[ '1 pos', '2 pos', '3 pos', '4 pos', '5 pos' ]
Anothe example using objects:
> var obj = [{name: 'jos', age: 12}, {name: 'nika', age: 23}]
undefined
> obj
[ { name: 'jos', age: 12 }, { name: 'nika', age: 23 } ]
> obj.map(a => a)
[ { name: 'jos', age: 12 }, { name: 'nika', age: 23 } ]
> obj.map(a => a.name)
[ 'jos', 'nika' ]
> obj.map(a => a.age)
[ 12, 23 ]
> obj.map(a => a.name +' '+ a.age)
[ 'jos 12', 'nika 23' ]
Using Filter​
This method we use to filter a array, and in there we can add a condictional to filter it
> const array = [1, 23, 44, 5, 6, 76, 767]
undefined
> array.filter(v => v > 10)
[ 23, 44, 76, 767 ]
> array.filter(v => v > 40)
[ 44, 76, 767 ]
Using Reduce​
> const array2 = [1, 2, 3]
undefined
> array2.reduce((ac, val) => ac + val)
6
In this example, we are adding all number inside of array, that means, we are doing this
1+2+3, and then, to do that kind of operation, we can use reduce, where we are able to create operations and accumulate each result.reduce we can use 4 values in the parameter,
accumulate,values_array,index_value,current_array. In this example,acis the accumulate andvalis value
Concat​
This method will allow us to join arrays
> a = [1,2,3]
[ 1, 2, 3 ]
> b = [11,22,33]
[ 11, 22, 33 ]
> j = a.concat(b)
[ 1, 2, 3, 11, 22, 33 ]
> j
[ 1, 2, 3, 11, 22, 33 ]
Fill​
Example to how fill an array with a specific valor
> var aa = ['aa', 'bb', 'cc']
undefined
> aa.fill('xoxo')
[ 'xoxo', 'xoxo', 'xoxo' ]
> aa
[ 'xoxo', 'xoxo', 'xoxo' ]
Join​
Join allow us transform a array into a string, joing all the index
> var ww = ['aaaa', 'bbbbb', 'uuuuuu']
undefined
> ww.join(" ")
'aaaa bbbbb uuuuuu'
> ww.join("-")
'aaaa-bbbbb-uuuuuu'
> ww.join(" -*- ")
'aaaa -*- bbbbb -*- uuuuuu'
String manipulation​
Here we create a simple array with string
> var tt = ['sd', 'dasda', 'SADAD']
undefined
> tt
[ 'sd', 'dasda', 'SADAD' ]
Upper Case​
Here we will upper case the index 0
> tt[0].toUpperCase()
'SD'
And also we can lower case the index 2
Lower Case​
> tt[2].toLowerCase()
'sadad'
Anothe example, manipulating a string
> var st = 'AAAA SSSSS'
undefined
And then, we will replace that string AAAA
Replace​
> st.replace('AAAA', 'AXAX')
'AXAX SSSSS'
As we can see, the method replace works like that
replace(current_string, new_string)
Now we will se how to slice a string:
Slice​
> var st2 = st.replace('AAAA', 'AXAX')
undefined
> st2.slice(3)
'X SSSSS'
Here, the st2 is a variable where exists that string
AXAX SSSSS, so the slice will delete 3 characteres from the beginning, for example[AXA]X SSSSSIf we put -3 we will delete 3 characteres from the final
Using the split
Split​
> var aa = 'AAA SS DD'
undefined
> aa
'AAA SS DD'
Now we will split that string, to do that, we will put in the parameter of method, which kind of string we will use to separate a group of string. I will use the space to create a array of strings
> aa.split(" ")
[ 'AAA', 'SS', 'DD' ]
Let's suppose that we have a comma, and we will use that comma to be a reference to divide our group of string
> var bb = 'sasa, aa, dd, gg'
undefined
> bb
'sasa, aa, dd, gg'
> bb.split(",")
[ 'sasa', ' aa', ' dd', ' gg' ]
Repeat​
Now, how to use the repeat method:
> var hi = 'hi!'
undefined
> hi.repeat(3)
'hi!hi!hi!'
Search​
Search will show us the index of a string, if such string does not exist, the output will be -1
> var st = 'A bb ccc'
undefined
> st.search("bb")
2
> st.search("A")
0
> st.search("ccc")
5
As we can see, the
bbstring starts in the index 2, theAstarts in the index 0
> st.search("sssss")
-1
If the string does not exist, the output is -1
Trim​
Trim is interesting, because it will delete from our string, useless spaces
> var aa = ' sdad sad dasd '
undefined
> aa
' sdad sad dasd '
> aa.trim()
'sdad sad dasd'
We can notice that trim delete space from the beginning and end of the string
Functions​
Here a example using annonymous function and arrow function
> var x = () => 'hi'
undefined
> x
[Function: x]
> x()
'hi'
> var xx = function(){ return 'hello' }
undefined
> xx()
'hello'
> var ss = xx
undefined
> ss()
'hello'
Spread operator​
> const ax = (...a) => `${a} --`
undefined
> ax(112,23,34,45,65)
'112,23,34,45,65 --'
> const bx = (a) => `${a} -- `
undefined
> bx(121,231,231,3123,32,342)
'121 -- '
Spread operator
...allows us to add multiples args into the parameter
> const string = 'mariana'
undefined
> string
'mariana'
> const artring = [...string]
undefined
> artring
[
'm', 'a', 'r',
'i', 'a', 'n',
'a'
]
And also it allows us to transform a string into a array easily
> const ar = [1,2,3]
undefined
> const ar2 = [ar]
undefined
> ar2
[ [ 1, 2, 3 ] ]
> const ar3 = [...ar]
undefined
> ar3
[ 1, 2, 3 ]
Or avoid to add a array A into another array B, but transform the array A as a B