The ultimate JavaScript cheatsheet you'll ever need

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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

    ```js for (var i = 0; i < 10; i++) { console.log(i + ": " + i * 3 + "
    "); }

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);


- While Loop

  ```js
  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 = "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

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" + "" + "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

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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Comments (2)

David Pavlicko's photo

Nice cheat sheet, did notice some type errors on the first for Loop:

here's the corrected code:

for (var i = 0; i < 10; i++) {
    console.log(i + ": " + i * 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);
DevWriteups.com's photo

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