JavaScript CheatSheet 2021
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 hexColor(c){
if(c < 256){
return Math.abs(c).toString(16);
}
return 0;
}
console.log(hexColor(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; i < 10; i++){
console.log(i + ": " + i * 3 + "<br />";
}
// 0: 0
// 1: 3
// ...
let a = [1,2,3];
var sum = 0;
for (var i = 0; i < a.length; i++){
sum += a[i];
}
console.log(sum); // 6
While Loop
var i = 1;
while(i < 100){
i *= 2;
console.log(i + ", ");
}
// 2,
// 4,
// ...
// 128,
Do While Loop
var i = 1;
while (i < 100) {
i *= 2;
console.log(i + ", ");
} 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 + ", ");
}
// 0,
// 1,
// ...
// 4,
Continue
for (var i = 0; i < 10; i++){
if(i == 5){
continue; // skips the rest of the cycle
}
console.log(i + ", ");
}
// 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 // -> Array(4) ["brocxoli", "cauliflower", "cabbage", "kale"]
console.log(plants);
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.getFullYear()); // (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
?? Thanks For Reading | Happy Coding?