ES6 Flashcards
What is a code block? What are some examples of a code block?
Blocks are notated by curly braces, loops often times
What does block scope mean?
Means that the variable within the block will not be accessible from outside the block.
What is the scope of a variable declared with const or let?
Block scope
What is the difference between let and const?
let ‘s value can be reassigned const can not.
Why is it possible to .push() a new value into a const variable that points to an Array?
Because we can change the arrays elements but we cannot reassign the const variable to a new array.
How should you decide on which type of declaration to use?
if the value needs to be reassigned, use let, otherwise use const.
What is the syntax for writing a template literal?
` text ${expression}`
What is “string interpolation”?
the JavaScript engine will automatically replace these variables ${} and expressions with their values
What is destructuring, conceptually?
were taking properties or array element values, extracting them to their own variables.
What is the syntax for Object destructuring?
let {propKey1: propAlias1, lastname} = object.
What is the syntax for Array destructuring?
let [x,y,z] = array
How can you tell the difference between destructuring and creating Object/Array literals?
the curly brackets are on the left side of the assignment operator.
What is the syntax for defining an arrow function?
(param1, param2) => {
return;
}
param => exp;
() => exp;
When an arrow function’s body is left without curly braces, what changes in its functionality?
evaluated as an expression not a statement. result of that expression is returned, implicit return.
How is the value of this determined within an arrow function?
lexically, it takes the this from the enclosing function. it is determined at definition for arrow functions. call time for es5 functions.
What are the three states a Promise can be in?
pending: initial state, neither fulfilled nor rejected.
fulfilled: meaning that the operation was completed successfully.
rejected: meaning that the operation failed.
state cannot be changed
How do you handle the fulfillment of a Promise?
How do you handle the rejection of a Promise?
The then() method returns a Promise. It takes up to two arguments: callback functions for the success and failure cases of the Promise.
How do you handle the fulfillment of a Promise?
The catch() method returns a Promise and deals with rejected cases only. you pass it a callback function
What is “syntactic sugar”?
syntactic sugar is syntax within a programming language that is designed to make things easier to read or to express.
What is the typeof an ES6 class?
a function
Describe ES6 class syntax.
class Person {
optional constructor(name) {
this.name = name;
}
getName() {
return this.name;
}
}What is “refactoring”?
code refactoring is the process of restructuring existing computer code—changing the factoring—without changing its external behavior. Refactoring is intended to improve the design, structure, and/or implementation of the software (its non-functional attributes), while preserving its functionality
How are ES Modules different from CommonJS modules?
ES modules are the standard for JavaScript, while CommonJS is the default in Node. js.
the way you import and export them.
import keyword
export default class name
What kind of modules can Webpack support?
ECMAScript modules. CommonJS modules. AMD modules.
