the murmurous sea

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode Strict mode JavaScript's strict mode, introduced in ECMAScript 5, is a way to opt in to a restricted variant of JavaScript, thereby implicitly opting-out of "sloppy mode". Strict mode isn't just a subset: it intentionally has different semantics from normal code. Brow developer.mozilla.org https://m.blog.naver.com/on21..

The study started from: I can't hoist const function...?! Why...? A. Declaring Variables www.youtube.com/watch?v=dzEieWaOJE0&t=5s www.youtube.com/watch?v=j-9_15QBW2s B. Temporal Dead Zone It's because of : Unlike variables declared with var, which will start with the value undefined, let variables are not initialized until their definition is evaluated. : Accessing the variable before the initia..

What is Event? - The Event interface represents an event which takes place in the DOM. - An event can be triggered by the user action or can also be triggered programmatically. - Event itself contains the properties and methods which are common to all events. - 이벤트는 이벤트 대상, 이벤트 종류, 이벤트가 발생했을 때 실행되는 함수, 이 3가지로 구성 Constructor Event() How to add 1. HTML tag - inline: add the function to the tag pro..

https://developer.mozilla.org/en-US/docs/Web/API/EventTarget/addEventListener

After //1. var console.log('typeof minus:', typeof minus) console.log('minus(5,1):', minus(5,1)) var minus = (a,b) => a - b; //typeof minus: undefined //Uncaught TypeError: minus is not a function at check.js:4 //(anonymous) @ check.js:4 //2. const console.log('typeof minus:', typeof minus) console.log('minus(5,1):', minus(5,1)) const minus = (a,b) => a - b; //Uncaught ReferenceError: Cannot acc..

Object.keys() 1. method 2. iterated in the same order that a normal loop would. [Syntax] Object.keys(obj) [Return Value] An array : of strings : of a given object's own enumerable property names : that represent all the enumerable properties of the given object. : The ordering of the properties is the same as the obj. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objec..

[Background] Functions are Objects : In Javascript, functions are first-class objects. : can work in the same way with other objects, like assigning them to variables and passing them as arguments into other functions. [Why use this] Most of the programs and applications operate in a synchronous manner. When we don't know when data will be served back(such as an external API), we want to wait fo..

1. method 2. creates a new array filled with all array elements that pass a test (provided as a function). 3. does not execute the function for array elements without values. 4. does not change the original array. [Syntax] let newArray = arr.filter(callback(element[, index, [array]])[, thisArg]) ▽ callback Required A function to be run for each element in the array. is a predicate, to test each ..

forEach() 1. method 2. executes a provided function once for each array element, in order. 3. for array elements without values? [Syntax] arr.forEach(callback(currentValue [, index [, array]])[, thisArg]) ▽ callback Required Function to execute on each element in the array. function(currentValue, index, arr) currentValue Required. The current element being processed in the array. index Optional...