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
  

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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,
  

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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.
  

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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
  

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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

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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

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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

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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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