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ES6 Basics
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1/25 Constants are block-scoped variables.
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2/25 The statement "let" declares a block scope local variable.
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3/25 What is the final value of "obj" in the following example?
const obj = { foo: 1 };
obj.bar = 2; -
4/25 What value will this expression return?
[...[...'...']].length -
5/25 What will the result of this expression be?
typeof (new (class F extends (String, Array) { })).substring -
6/25 What will this function return?
(function() {
if (false) {
let f = { g() => 1 };
}
return typeof f;
})() -
7/25 What result will this expression have?
typeof (function* f() { yield f })().next().next() -
8/25 Why is super used?
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9/25 ES6 introduces a special "const" declaration. Do you know what it does?
const PI = 3.14;
console.log(PI) //Prints 3.14 -
10/25 ES6 gives you a number of new methods for operating with Strings. Which one replaces this annoying piece of code?
let some_text = "some string";
if(some_text.indexOf('str') !=-1){
return true;
} -
11/25 Array.from() is a powerful method which converts array-like objects into real Arrays. Why do you use it in the code below?
let titleElements = document.querySelectorAll('.article .title') let titles = Array.from(titleElements).map( t => t.textContent ); console.log(titles); -
12/25 ES6 gives an alternative way to assign variables. Can you guess what the below code does?
let a = 12, b = 3;
[a, b] = [b, a]; -
13/25 Is this a valid code?
class Slave { // ... };
const slave = Slave(); -
14/25 In ES6, which keyword is used to import modules?
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15/25 What is the output of the following code snippet? `const [a, , b] = [1, 2, 3]; console.log(a, b);`
const [a, , b] = [1, 2, 3];
console.log(a, b); -
16/25 Which ES6 feature allows for declaring read-only named constants?
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17/25 Which ES6 feature is used to write expressions in a more concise way?
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18/25 How does 'const' behave differently from 'var' in ES6?
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19/25 What is the main advantage of using 'let' over 'var' in ES6?
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20/25 Which new data structure introduced in ES6 stores unique values of any type?
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21/25 In ES6, which statement correctly imports a single export from a module?
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22/25 In ES6, what is the main use of a 'Symbol'?
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23/25 How does 'yield' work in ES6?
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24/25 In ES6, what is the result of using a template literal inside another template literal?
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25/25 How does the 'endsWith()' method work with ES6 strings?
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It seems you haven't answered any questions yet. Please provide your answers to proceed.