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# Ultimate JavaScript CheatSheet

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.

### 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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😎Thanks For Reading | Happy Coding⚡

Get weekly newsletter of amazing articles i posted this week and some offers or announcement. Subscribe from Here ## Discussion (15) Okoro Redemption

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 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. Shwetabh Shekhar

This is great. Thanks for sharing! Scipion

Do while snippet is wrong. In line 2 should be a "do" instead of a "while". Also the condition in last line, "(1 < 100)" makes an infinite loop, it seems it should be "i" instead of "1".

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