Rahul

Posted on Jan 12, 2021 • Edited on Dec 1, 2022

Ultimate JavaScript CheatSheet

#beginners #codenewbie #javascript #webdev

Cheat Sheets our something developers need always for reference. So here I have compiled many JavaScript reference codes. See the classification and find it. This post is helpful for learners and developers.

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JavaScript Number Method Cheat Sheet

toExponential() : Returns a string representing the Number object in exponential notation

  function expo(x, f) {
      return 
      Number.parseFloat(x).toExponential(f);
  }

  console.log(expo(123456, 2)); 
  // -> 1.23e+5

toFixed() : formats a number using fixed-point notation

  function financial(x) {
      return Number.parseFloat(x).toFixed(2); 
  }

  console.log(financial(123.456)); 
  // -> 123.46

toPrecision() : returns a string representing the Number object to the specified precision

  function precise(x) {
      return
      Number.parseFloat(x).toPrecision(4); 
  }

  console.log(precise(123.456)); 
  // -> 123.5

toString() : returns a string representing the specifies Number object

  function hexColour(c) {
      if (c < 256) {
          return Math.abs(c).toString(16); 
      }
      return 0; 
  }

  console.log(hexColour(233)); 
  // -> e9

valueOf() : returns the wrapped primitive value of a number object

  const numObj = new Number(42); 
  console.log(typeof numObj); 
  // -> object

  const num = numObj.valueOf(); 
  console.log(num); 
  // -> 42

  console.log(typeof num); 
  // -> number

JavaScript Loops Cheat Sheets

For Loop

  for (var i = 0; < 10; i++) {
      console.log(i + ": " + i * 3 + "<br />"); 
  }
  // -> 0: 0<br />
  // -> 1: 3<br />
  // -> ...

  let a = [1, 2, 3]; 
  var sum = 0; 
  for (var i - 0; i <a.length; i++) {
      sum += a[i]; 
  } // pasing an array
  console.log(sum); 
  // -> 6

While Loop

  var i = 1;                  // initialize
  while (i < 100) {          // enters the cycle if statement is true
      i *= 2;                 // increment to avoid infinte loop 
      console.log(i + ", "); // output
  } 
  // 2, 
  // 4, 
  // ...
  // 128,

Do While Loop

  var i = 1;                  // initialize
  while (i < 100) {          // enters the cycle asleast once
      i *= 2;                 // increment to avoid infinte loop 
      console.log(i + ", "); // output
  } while (1 < 100); // repeats cycle if statement is true at the end
  // 2, 
  // 4, 
  // ...
  // 128,

Break

  for (var i = 0; i < 10; i++) {
      if (i == 5 ) { break; } // stops and exits the cycle
      console.log(i + ", ");  // Lat output number is 4
  }
  // -> 0, 
  // -> 1, 
  // ...
  // -> 4,

Continue

  for (var i = 0; i < 10; i++) {
      if (i == 5 ) { continue; } // skips the rest of the cycle
      console.log(i + ", ");  // skips 5
  }
  // -> 0, 
  // -> 1, 
  // ...
  // -> 9,

JavaScript String Methods Cheat Sheet

charAt() : Returns the character at the specified index

  const sentence = "Jeff bezos is now the second richest."; 

  const index = 4; 

  console.log(`The character at index ${index} is ${sentence.charAt(index)}`); 
  // The character at index 4 is f

concat() : Joins two or more strings, and returns a copy of the joined strings

  const str1 = "Hello"; 
  cosnt str2 = "World"; 

  console.log(str1.concat(" ", str2)); 
  // -> Hello World

  console.log(str2.concat(", ", str1)); 
  // -> World, Hello

replace() : Searches for a match between a substring (or regex) and a string and replaces the matched substring with a new substring

  const p = "Talk is cheap. Show me the work. - Someone"; 

  console.log(p.replace("work", "code")); 
  // -> Talk is cheap. Show me the code. - Someone

search() : Searches for a match between a regex and a string, and returns the position of the match

  const paragraph = "The quick brown fox jumps over the lazy dog."; 

  // any character that is not a word character or whitespace
  const regex = /[^\w\s]/g;

  console.log(paragraph.search(regex)); 
  // -> 43

slice() : Extracts a part of a string and returns a new string

  const str = "The quick brown fox jumps over the lazy dog."; 

  consolelog(str.slice(31)); 
  // -> the lazy dog

  console.log(str.slice(4, 19)); 
  // -> quick brown fox

trim() : Removes whitespace from both ends of a string

  const greeting = "  Hello world!   "; 

  console.log(greeting); 
  // -> Hello world!

  console.log(greeting.trim()); 
  // -> Hello world!

substr() : Extracts the character from a string, beginning at a specified start position, and through the specified number of character

  const str = "Mozilla"; 

  console.log(str.substr(1, 2)); 
  // -> oz

  console.log(stre.substr(2)); 
  // -> zilla

toLowerCase() : Converts a string to lowercase letters

  const sentence = "Elon became the richest last night."; 

  console.log(sentence.toLowerCase()); 
  // -> elon became the richest last night.

JavaScript Array Method Cheet sheet

concat() : Joins two or more arrays, and returns a copy of the joined array

  let array1 = ["a", "b", "c"]; 
  let array2 = ["d", "e", "f"]; 
  let array3 = array1.concat(array2); 

  console.log(array3); 
  // -> Array(6) ["a", "b", "c", "d", "e", "f" ]

indexOf() : Search the array for an element and returns its position

  let beasts = ["ant", "bison", "camel", "duck", "bison"]; 

  console.log(beasts.indexOf("bison")); 
  // -> 1

  // start from index 2
  console.log(beasts.indexOf("bison", 2)); 
  // -> 4

join() : Joins all elements of an array into a string

  let elements = ["Fire", "Air", "Water"]; 

  console.log(elements.join()); 
  // -> Fire,Air,Water

  console.log(elements.join(" ")); 
  // -> Fire Air Water

pop() : Removes the last element of an array, and returns that element

  let plants = ["broccoli", "cauliflower", "cabbage", "kale", "tomato"]; 

  console.log(plants.pop()); 
  // -> tomato

  console.log(plants); 
  // -> Array(4) ["brocxoli", "cauliflower", "cabbage", "kale"]

reverse() : Reverses the order of the elements in an array

  let array1 = ["one", "two", "three"]; 
  console.log("array1:", array1); 
  // -> array1: Array(3) [ "one", "two", "three" ]

  let reversed = array1.reverse(); 
  console.log("reversed", reversed); 
  // -> reversed: Array(3) [ "three", "two", "one" ]

shift() : Removes the first element of an array, and returns that element

  let array1 = [1, 2, 3]; 

  let firstElement = array1.shift(); 

  console.log(array1); 
  // -> Array [ 2, 3 ]

sort() : Sorts the element of an array

  let months = ["March", "Jan", "Feb", "Dec"]; 
  months.sort(); 

  console.log(months); 
  // -> Array(4) [ "Dec", "Feb", "Jan", "March" ]

toString() : Converts an array to string, and returns the result

  const array1 = [1, 2, "a", "1a"]; 

  console.log(array1.toString()); 
  // -> 1,2,a,1a

JavaScript Datatypes Cheat Sheet

var age = 18; // Number

var name = "Rahul"; // string

var name = {first:"Rahul", last:"Singh"}; // object

var truth = false; // boolean

var sheets = ["HTML", "CSS", "JS"]; // array

var a; typeof a; // undefined 

var a = null; // value null

JavaScript Operators Cheat Sheet

a = b + c - d; // addition, substraction

a = b * (c / d); // multiplication, division

x = 100 % 48; // modulo. 100 / 48 remainder = 4

a++; b--; // postfix increment and decrement

Variables cheat sheet

var : The most common variable. Can be reassigned but only accessed within a function. Variables defined with var move to the top when code is executed.
const : Cannot be reassigned and not accessible before they appear within the code
let : Similar to const, however, let variable can be reassigned but not re-declared

var a;            // variable
var b = "init";   // string
var c = "Hi" + "" + "Rahul"; // "Hi Rahul"
var d = 1 + 2 + "3";   // "33"
var e = [2,3,5,8];   // array
var f = false;       // boolean
var g = /()/; // RegEx
var h = function(){};   // function object
const PI = 3.14;        // constant
var a = 1, b = 2, c = a + b;    // one line
let z = 'zzz';        // block scope local variable

Get Date Methods Cheet Sheet

getFullYear() : Returns the year of the specified date according to local time

  const moonLanding = new Date("January 08, 69 00:20:10"); 

  console.log(moonLanding.getFullYear()); 
  // -> 1969

getMonth() : Returns the month in the specified date according to local time, as a zero-based value (where zero indicates the first month of the year).

  const moonLanding = new Date("January 08, 69 00:20:10"); 

  console.log(moonLanding.getMonth()); // (January gives 0)
  // -> 6

getDate() : Returns the day of the month for the specified date according to local time

  const birthday = new Date("June 16, 2004 23:14:00"); 
  const date1 = birthday.getDate(); 

  console.log(date1); 
  // -> 19

getHours() : Returns the hour for the specified date, according to local time

  const birthday = new Date("June 16, 04 4:20"); 

  console.log(birthday.getHours()); 
  // -> 4

getMinutes() : Returns the minutes in the specified date according to local time

  const birthday = new Date("June 16, 04 04:10"); 

  console.log(birthday.getMinutes());
  // -> 20

getSeconds() Returns the seconds in the specified date according to local time

  const moonLanding = newDate("June 16, 69 00:23:11"); 

  console.log(moonLanding.getSeconds()); 
  // -> 18

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Top comments (15)

Marcel • Jan 14 '21

Hey, great article! Just one thing the "charAt()" example actually returns an empty space " ", not a "f"

Rahul • Jan 14 '21

Agreed.

Thank for reading i am happy i have someone to read too.

Garrett McCullough • Jan 13 '21

your toExponential and toPrecision examples are broken. If a return statement is on a line by itself, it will just return undefined.

Okoro Redemption • Jan 18 '21

Beautiful Post.

Check out this Utility JavaScript Library I made that is sure to ease your workflow.
It contains methods and functions that manipulates the DOM, Strings, Numbers, Objects and even Mathematical operations, and other utility functions

Its called ToolJS and can be found on Github and NPM

npm install @redeakaa/tooljs

You can check out this series I posted here on dev.to

Introduction to ToolJS. A JavaScript Utility Library

Comment hidden by post author - thread only accessible via permalink

Mateusz Kwiatkowski • Jan 12 '21

It seems like the whole "the 2021" part of the article is missing. I don't want to be rude but all here is like fundamentals of JS and not some bright new features, which could help one in 2021. For that reason I would say the article's title is misleading at best and a clickbait at worst.