Salesforce JavaScript-Developer-I 問題集

質問 1：
developer is trying to convince management that their team will benefit from using Node.js for a backend server that they are going to create. The server will be a web server that handles API requests from a website that the teamhas already built using HTML, CSS, and JavaScript.
Which three benefits of Node.js can the developer use to persuade their manager?
Choose 3 answers:
A. Uses non-blocking functionality for performant requesthandling .
B. Performs a static analysis on code before execution to look for runtime errors.
C. Executes server-side JavaScript code to avoid learning a new language.
D. Ensures stabilitywith one major release every few years.
E. Installs with its own package manager to install and manage third-party libraries.
正解：A,B,E

質問 2：
A developer needs to test this function:
01const sum3 = (arr) => (
02if (!arr.length) return 0,
03if (arr.length === 1) return arr[0],
04if (arr.length === 2) return arr[0]+ arr[1],
05 return arr[0] + arr[1] + arr[2],
06 );
Which two assert statements are valid tests for the function?
Choose 2 answers
A. console.assert(sum3(0)) == 0);
B. console.assert(sum3(1, '2')) == 12);
C. console.assert(sum3('hello', 2, 3, 4)) === NaN);
D. console.assert(sum3(-3, 2 )) == -1);
正解：B,D

質問 3：

Which code change should be done for the console to log the following when 'Click me!' is clicked'
> Row log
> Table log
A. Change line 14 to elem.addEventListener ('click', printMessage, true);
B. Remove line 10
C. Remove lines 13 and14
D. Change line 10 to event.stopPropagation (false) ;
正解：B

質問 4：
is below:
<input type="file" onchange="previewFile()">
<img src="" height="200" alt="Image Preview..."/>
The JavaScript portion is:
01 functionpreviewFile(){
02 const preview = document.querySelector('img');
03 const file = document.querySelector('input[type=file]').files[0];
04 //line 4 code
05 reader.addEventListener("load", () => {
06 preview.src = reader.result;
07 },false);
08 //line 8 code
09 }
In lines 04 and 08, which code allows the user to select an image from their local computer , and to display the image in the browser?
A. 04 const reader = new FileReader();08 if (file) reader.readAsDataURL(file);
B. 04 const reader = new File();08 if (file) URL.createObjectURL(file);
C. 04 const reader = new FileReader();08if (file) URL.createObjectURL(file);
D. 04 const reader = new File();08 if (file) reader.readAsDataURL(file);
正解：A

質問 5：
A developer at Universal Containers creates a new landing page based on HTML, CSS, and JavaScript TO ensure that visitors have a goodexperience, a script named personaliseContext needs to be executed when the webpage is fully loaded (HTML content and all related files ), in order to do some custom initialization.
Which statement should be used to call personalizeWebsiteContent based onthe above business requirement?
A. window.addEventListener('load',personalizeWebsiteContext);
B. Document.addEventListener('''DOMContextLoaded' , personalizeWebsiteContext);
C. window.addEventListener('onload', personalizeWebsiteContext);
D. document.addEventListener(''onDOMContextLoaded', personalizeWebsiteContext);
正解：A

質問 6：
Refer to the following code block:

What is the console output?
A. > Jackie got 70% on test.
B. > Uncaught Reference Error
C. > Better student Jackie got 100% on test.
D. > Better student Jackie got 70% on test.
正解：C

質問 7：
Refer to the code below:
const event = new CustomEvent(
//Missing Code
);
obj.dispatchEvent(event);
A developer needs to dispatch a custom event called update to send information about recordId.
Which two options could a developer insert at the placeholder in line 02 to achieve this?
Choose 2 answers
A. { type : 'update', recordId : '123abc' }
B. 'Update' , (recordId : '123abc'(
C. 'Update' , {Details : {recordId : '123abc'}}
D. 'Update' , '123abc'
正解：B,C

質問 8：
Refer to code below:
Const objBook = {
Title: 'Javascript',
};
Object.preventExtensions(objBook);
Const newObjBook = objBook;
newObjectBook.author ='Robert';
What are the values of objBook and newObjBook respectively ?
A. {author: "Robert"}{author: "Robert", title: "javaScript}
B. [title: "javaScript"] [title: "javaScript"]
C. {author: "Robert", title: "javaScript}Undefined
D. {author: "Robert", title: "javaScript}{author: "Robert", title: "javaScript}
正解：B

質問 9：
A developer implements and calls the following code when an application state change occurs:
Const onStateChange =innerPageState) => {
window.history.pushState(newPageState, ' ', null);
}
If the back button is clicked after this method is executed, what can a developer expect?
A. The page reloads and all Javascript is reinitialized.
B. The page isnavigated away from and the previous page in the browser's history is loaded.
C. A popstate event is fired with a state property that details the application's last state.
D. A navigate event is fired with a state property that details the previous application state.
正解：B