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| Section | Weight | Objectives |
|---|---|---|
| Topic 1: Server Side JavaScript | 8% | - Node.js fundamentals and core modules - Package management and CLI tools |
| Topic 2: Debugging and Error Handling | 7% | - Error types and handling strategies - Console usage, breakpoints and debugging techniques |
| Topic 3: Objects, Functions, and Classes | 25% | - ES6 classes, inheritance, modules, decorators - Object creation, properties, prototypes - Function types, scope, closures, arrow functions |
| Topic 4: Browser and Events | 17% | - DOM selection and manipulation - Browser APIs and developer tools - Event handling, propagation, listeners |
| Topic 5: Variables, Types, and Collections | 23% | - Strings, numbers, dates, arrays and methods - Variable declaration and scope - JSON parsing and manipulation - Data types, type coercion, truthy/falsy values |
| Topic 6: Testing | 7% | - Unit test structure and effectiveness - Test coverage and improvement |
| Topic 7: Asynchronous Programming | 13% | - Callbacks, promises, async/await - Event loop and execution flow |
為什麼大多數人選擇Fast2test，是因為Fast2test的普及帶來極大的方便和適用。是通過實踐檢驗了的，Fast2test提供 Salesforce的JS-Dev-101考試認證資料是眾所周知的，許多考生沒有信心贏得 Salesforce的JS-Dev-101考試認證，擔心考不過，所以你得執行Fast2test Salesforce的JS-Dev-101的考試培訓資料，有了它，你會信心百倍，真正的作了考試準備。
問題 #121
Refer to the code below (corrected to use a template literal on line 08):
01 let car1 = new Promise((_, reject) =>
02 setTimeout(reject, 2000, "Car 1 crashed in")
03 );
04 let car2 = new Promise(resolve =>
05 setTimeout(resolve, 1500, "Car 2 completed")
06 );
07 let car3 = new Promise(resolve =>
08 setTimeout(resolve, 3000, "Car 3 completed")
09 );
10
11 Promise.race([car1, car2, car3])
12 .then(value => {
13 let result = `${value} the race.`;
14 })
15 .catch(err => {
16 console.log("Race is cancelled.", err);
17 });
What is the value of result when Promise.race executes?
答案：A
解題說明：
Comprehensive and Detailed Explanation From Exact Extract JavaScript knowledge:
Understand the three promises:
car1:
let car1 = new Promise((_, reject) =>
setTimeout(reject, 2000, "Car 1 crashed in")
);
Rejects after 2000 ms (2 seconds) with message "Car 1 crashed in".
car2:
let car2 = new Promise(resolve =>
setTimeout(resolve, 1500, "Car 2 completed")
);
Resolves after 1500 ms (1.5 seconds) with message "Car 2 completed".
car3:
let car3 = new Promise(resolve =>
setTimeout(resolve, 3000, "Car 3 completed")
);
Resolves after 3000 ms (3 seconds) with message "Car 3 completed".
Promise.race:
Promise.race([car1, car2, car3])
.then(value => {
let result = `${value} the race.`;
})
.catch(err => {
console.log("Race is cancelled.", err);
});
Behavior of Promise.race:
It settles (resolves or rejects) as soon as any of the given promises settles.
It uses the value or reason from the first settled promise.
Timing:
car2 resolves in 1500 ms.
car1 rejects in 2000 ms.
car3 resolves in 3000 ms.
The first to settle is car2 at 1500 ms, with value "Car 2 completed".
Therefore:
Promise.race resolves (not rejects) with value = "Car 2 completed".
The .then handler runs; .catch is ignored because there is no rejection.
Inside .then:
let result = `${value} the race.`;
Substitute value:
let result = "Car 2 completed the race.";
So, result becomes:
Car 2 completed the race.
Compare to options:
A . Car 3 completed the race.
This would be correct if car3 were the first to resolve, which it is not (it resolves last).
B . Car 2 completed the race.
Exactly matches the first-resolving promise and the constructed message.
C . Race is cancelled.
This is the prefix of the string logged in the .catch handler, but .catch never runs because the race resolves, it does not reject first.
D . Car 1 crashed in the race.
car1 is the first rejection, but since a resolution from car2 happens earlier, the race is already settled successfully before car1 rejects.
Thus the correct value of result as set in the .then block is:
Answe r: B
Study Guide / Concept Reference (no links):
Promise.race(iterable) semantics (first settled promise wins)
setTimeout and timing interactions with Promises
Resolve vs reject paths and .then / .catch
Template literals and string interpolation for building result messages
問題 #122
At Universal Containers, every team has its own way of copying JavaScript objects. The code snippet shows an implementation from one team:
01 function Person() {
02 this.firstName = "John";
03 this.lastName = "Doe";
04 this.name = () => {
05 console.log('Hello ${this.firstName} ${this.lastName}');
06 }
07 }
08
09 const john = new Person();
10 const dan = JSON.parse(JSON.stringify(john)); // (intended deep copy)
11 dan.firstName = 'Dan';
12 dan.name();
(Original line 10 is logically intended to be JSON.parse(JSON.stringify(john)) to perform a JSON clone.) What is the output of the code execution?
答案：C
解題說明：
JSON.stringify(john) converts the john object into a JSON string.
When you JSON.parse that string back, you get a plain object:
Only data that can be represented in JSON is preserved (numbers, strings, booleans, arrays, plain objects).
Functions are not preserved and are dropped.
So dan is a plain object with properties firstName and lastName, but no name method.
Therefore, dan.name is undefined, and dan.name() throws:
TypeError: dan.name is not a function
The literal string interpolation inside console.log('Hello ${...}') is also wrong (single quotes), but the code never reaches that line.
問題 #123
Refer to the code declarations below:
let str1 = 'Java';
let str2 = 'Script';
Which three expressions return the string JavaScript?
答案：A,B,D
解題說明：
The correct answers are A, B, and D.
The two variables are:
let str1 = 'Java';
let str2 = 'Script';
The goal is to combine them into:
JavaScript
Option A is correct because template literals can insert variables directly into a string:
`${str1}${str2}`
This becomes:
`${'Java'}${'Script'}`
Result:
JavaScript
Option B is correct because strings have a concat() method:
str1.concat(str2);
This joins str2 onto the end of str1.
Result:
JavaScript
Option D is correct because the + operator performs string concatenation when both operands are strings:
str1 + str2;
This becomes:
'Java' + 'Script'
Result:
JavaScript
The incorrect options:
Option C is not valid JavaScript for joining strings. const is used for declaring constants, not concatenating values.
Option E is incorrect because join() is an array method, not a string method. This would only work with an array, for example:
['Java', 'Script'].join('');
But str1 is a string, so:
str1.join(str2)
is invalid.
Therefore, the verified answers are A, B, and D.
問題 #124
Refer to the code below:
Async funct on functionUnderTest(isOK) {
If (isOK) return 'OK';
Throw new Error('not OK');
)
Which assertion accurately tests the above code?
答案：D
問題 #125
developer wants to use a module named universalContainersLib and them callfunctions from it.
How should a developer import every function from the module and then call the functions foo and bar ?
答案：B
問題 #126
......
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