ReasonJun

console // console //? .log(), .warn(), .error(), .dir() // -log : general message // -warn : warning message // -error : error message // -dir : Output an object whose properties can be viewed console.log(document.body); console.warn(document.body); console.error(document.body); console.dir(document.body); //? .count(), .countReset() // Prints or initializes the cumulative number of console met..

In JavaScript, a Symbol is a primitive data type introduced in ECMAScript 2015 (ES6). It is a unique and immutable value that can be used as an identifier for object properties. Symbols are often used as keys in objects to avoid naming conflicts and ensure uniqueness. const mySymbol = Symbol(); // create a Symbol using the Symbol() function const mySymbol = Symbol('My Symbol'); // Symbols can al..

In JavaScript, a Map is a built-in data structure that allows you to store key-value pairs, where both the keys and values can be of any type. It provides an efficient way to associate values with unique keys and perform operations such as insertion, retrieval, and deletion. const myMap = new Map(); // creating a new Map const myMap = new Map([ // initialize a Map ['key1', 'value1'], ['key2', 'v..

set In JavaScript, a Set is a built-in data structure that allows you to store unique values of any type. It provides a way to store a collection of values without any duplicates. The values in a Set can be of any type, including primitives like numbers and strings, as well as objects and other sets. const mySet = new Set(); // creating a new Set const mySet = new Set([1, 2, 3, 3, 4, 5, 5]); // ..

mouse pointer event // Mouse & Pointer Events // click // dbclick : double click // mousedown : press the button // mouseup : release the button // mouseenter : When the pointer goes over an element // mouseleave : when the pointer goes out of the element // mousemove : when the pointer moves // contextmenu : when right-clicked // wheel :When the wheel button rotates const parentEl = document.qu..

handler once / passive // Handler run only once const parentEl = document.querySelector('.parent'); parentEl.addEventListener( 'click', (event) => { console.log('parent'); }, { once: true, } ); // Separation of default behavior and handler execution // The execution itself may be slow because there are many actions on the webpage, but the user's manipulation of the webpage proceeds smoothly. par..