JavaScript-Developer-I 試験問題を無料オンラインアクセス

Corrected code:
let obj = {
foo: 1,
bar: 2
};
let output = [];
for (let something in obj) {
output.push(something);
}
console.log(output);
What is the output of line 11?

• A.[1, 2]
• B.[ " foo " , " bar " ]
• C.[ " foo:1 " , " bar:2 " ]
• D.[ " bar " , " foo " ]

A developer creates a class that represents a news story based on the requirements that a Story should have a body, author, and view count. The code is shown below:
01 class Story {
02 // Insert code here
03 this.body = body;
04 this.author = author;
05 this.viewCount = viewCount;
06 }
07 }
Which statement should be inserted in the placeholder on line 02 to allow for a variable to be set to a new instance of a Story with the three attributes correctly populated?

• A.function Story(body, author, viewCount) {
• B.super(body, author, viewCount) {
• C.constructor() {
• D.constructor(body, author, viewCount) {

A developer is setting up a new Node.js server with a client library that is built using events and callbacks.
The library:
* Will establish a web socket connection and handle receipt of messages to the server.
* Will be imported with require, and made available with a variable called ws.
* The developer also wants to add error logging if a connection fails.
Given this information, which code segment shows the correct way to set up a client with two events that listen at execution time?

• A.ws.on( ' connect ' , () = > {
  console.log( ' Connected to client ' );
  });
  ws.on( ' error ' , (error) = > {
  console.log( ' ERROR ' , error);
  });
• B.ws.on( ' connect ' , () = > {
  console.log( ' Connected to client ' );
  });
  ws.on( ' error ' , (error) = > {
  console.log( ' ERROR ' , error);
  });
• C.ws.connect(() = > {
  console.log( ' Connected to client ' );
  }).catch((error) = > {
  console.log( ' ERROR ' , error);
  });
• D.try {
  ws.connect(() = > {
  console.log( ' Connected to client ' );
  });
  } catch(error) {
  console.log( ' ERROR ' , error);
  }

Given a value, which two options can a developer use to detect if the value is NaN?

• A.isNaN(value)
• B.Object.is(value, NaN)
• C.value === Number.NaN
• D.value == NaN

Refer to the code below:
01 let o = {
02 get js() {
03 let city1 = String( ' St. Louis ' );
04 let city2 = String( ' New York ' );
05
06 return {
07 firstCity: city1.toLowerCase(),
08 secondCity: city2.toLowerCase(),
09 }
10 }
11 }
What value can a developer expect when referencing o.js.secondCity?

• A.An error
• B.undefined
• C.' new york '
• D.' New York '