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The ultimate JavaScript cheatsheet you'll ever need

Dev Write Ups
Group of Devs providing free resources to the beginners
Originally published at devwriteups.com ・5 min read

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
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  • toFixed() : formats a number using fixed-point notation
  function financial(x) {
      return Number.parseFloat(x).toFixed(2); 
  }

  console.log(financial(123.456)); 
  // -> 123.46
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  • 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
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  • 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
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  • 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
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  • 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, 
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  • 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,
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  • 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, 
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  • 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
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  • 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
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  • 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
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  • 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
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  • 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
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  • trim() : Removes whitespace from both ends of a string
  const greeting = "  Hello world!   "; 

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

  console.log(greeting.trim()); 
  // -> Hello world!
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  • 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
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  • 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" ]
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  • 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
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  • 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
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  • 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"]
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  • 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" ]
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  • 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 ]
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  • sort() : Sorts the element of an array
  let months = ["March", "Jan", "Feb", "Dec"]; 
  months.sort(); 

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

var name = {first:"Sam", 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" + "" + "Sam"; // "Hi Sam"
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

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  • 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
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  • 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
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  • 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
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  • 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
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  • 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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😎Thanks For Reading | Happy Coding⚡

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