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
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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Top comments (15)
Hey, great article! Just one thing the "charAt()" example actually returns an empty space " ", not a "f"
Agreed.
Thank for reading i am happy i have someone to read too.
your
toExponential
andtoPrecision
examples are broken. If areturn
statement is on a line by itself, it will just return undefined.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
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.
Hi. Just wanted to say that the example for getMonth() is using getFullYear().
Thanks for the useful article!
Nice! I made one for regex alone sometime back:
JavaScript regular expressions cheatsheet and examples
Sundeep ・ Dec 6 '19 ・ 8 min read
Great, thanks!
You have a mistake on your Do While Loop.
Awesome blog post, I already really like the new
includes
method for Strings and Arrays 🎉I think this is more complete as a reference: developer.mozilla.org/en-US/docs/W...
I will steal some of those snippets for my personal cheat sheet ;-) Thank you!
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".
Nice, now make this article into a cheatsheet!
Great article
This is great. Thanks for sharing!
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