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My DevNotes

CheatSheets

Some Basic

Comments

There are two types of comments: // this is a single line comment /_ this is a multiple line comment when you have to write a lot of things _/

// Single line comment
let name = "John";
/*
muliptle line comment
line comment.
Somecase also use disable code parts
*/
let fullname = "Doe";
let age = 35;

Variables

Variables – values that hold data to perform calculations or other operations

  • var - most widely used. can be accessed within the function where declared. can be reassigned.
  • const – constant value i.e. cannot be reassigned
  • let – can be used only within the block its declared, can be reassigned

Data types

Can be of different types

  • Number, eg. var id = 20
  • Unassigned variable, eg. var x
  • String, eg. var company = “hackr”
  • Boolean, eg. var windowopen = true
  • Constants. eg. const counter = 1
  • Operations, eg. var sum = 20 + 20
  • Objects, eg. var student = Contains single object of various data types

Arrays

Arrays group similar kinds of data together. Eg, var subjectlist = [“math”, “science”, “history”, “computer”];

More info: https://www.w3schools.com/js/js_arrays.asp

Arrays can perform the following functions:

More info:

https://www.w3schools.com/js/js_array_methods.asp

https://www.w3schools.com/jsref/jsref_obj_array.asp

FunctionsDescription
concat()Concatenate different arrays into one.
join()Joins all the elements of one array as a string
indexof()Returns the index (first position) of an element in the array
lastindexof()Returns the last position of an element in the array
sort()Alphabetic sort of array elements
reverse()Sort elements in descending order
valueof()Primitive value of the element specified
slice()Cut a portion of one array and put it in a new array
splice()Add elements to an array in a specific manner and position
unshift()Add new element to the array in the beginning
shift()Remove first element of the array
pop()Remove the last element of the array
push()Add new element to the array as the last one
tostring()Prints the string value of the elements of the array

Operators

Basic

  • Addition +
  • Subtraction -
  • Multiply *
  • Divide /
  • Remainder %
  • Increment ++
  • Decrement --
  • Execute brackets first …

Logical

  • And &&
  • Or ||
  • Not |

Comparison

  • Equal to ==
  • Equal value and type ===
  • Not equal !=
  • Not equal value or type !==
  • Greater than >
  • Less than <
  • Greater than or equal to >=
  • Less than or equal to <=
  • Ternary operator ?

Bitwise

  • AND &
  • OR |
  • NOT ~
  • XOR ^
  • Left shift <<
  • Right shift >>
  • Zero fill right shift >>>

continue later from here: https://hackr.io/blog/javascript-cheat-sheet#download-javascript-cheat-sheet