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⚡

Tags:#javascript#general-advice#web-development#hashnode
Kevin Pliester's photo

Great and thank you for that!

getMonth() would need to be rewritten again. Otherwise wonderful!

Reply
Ramya D's photo

Thanks, Rahul. Great Compilation🧡. Could you check and update the outputs of getMinutes() and getSeconds() and syntax & variable in do..while loop

Reply