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| Section | Weight | Objectives |
|---|---|---|
| Testing | 7% | - Unit test structure and effectiveness - Test coverage and improvement |
| Variables, Types, and Collections | 23% | - JSON parsing and manipulation - Data types, type coercion, truthy/falsy values - Strings, numbers, dates, arrays and methods - Variable declaration and scope |
| Server Side JavaScript | 8% | - Node.js fundamentals and core modules - Package management and CLI tools |
| Asynchronous Programming | 13% | - Event loop and execution flow - Callbacks, promises, async/await |
| Debugging and Error Handling | 7% | - Error types and handling strategies - Console usage, breakpoints and debugging techniques |
| Browser and Events | 17% | - Browser APIs and developer tools - Event handling, propagation, listeners - DOM selection and manipulation |
| Objects, Functions, and Classes | 25% | - Function types, scope, closures, arrow functions - ES6 classes, inheritance, modules, decorators - Object creation, properties, prototypes |
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NEW QUESTION # 121
Refer to the code below:
01 async function functionUnderTest(isOK) {
02 if (isOK) return 'OK';
03 throw new Error('not OK');
04 }
Which assertion accurately tests the above code?
Answer: A
Explanation:
The function:
async function functionUnderTest(isOK) {
if (isOK) return 'OK';
throw new Error('not OK');
}
Behavior:
If isOK is true:
The function resolves (fulfills the promise) with value 'OK'.
If isOK is false:
The function throws, which in an async function becomes a rejected promise with Error('not OK').
We want an assertion that accurately tests the successful path for isOK === true.
Key points about console.assert:
Signature: console.assert(condition, message?)
If condition is falsy, it logs message as an assertion failure.
If condition is truthy, nothing is logged.
We also must understand await:
await functionUnderTest(true) will resolve to the string 'OK'.
Now evaluate options.
Option A:
console.assert(await functionUnderTest(true), 'OK');
await functionUnderTest(true) → 'OK' (truthy).
console.assert('OK', 'OK');
Condition is 'OK' (truthy), so assertion passes.
The message 'OK' is only shown if the condition is falsy, which it is not.
This correctly verifies that the promise resolved (i.e., did not reject). Among the given options, this is the only one that both:
Uses await properly on the async function, and
Associates the message with the expected success "OK".
Option B:
console.assert(await (functionUnderTest(true), 'not OK'));
Inside the parentheses, the comma operator (a, b) evaluates a, discards it, and returns b.
So (functionUnderTest(true), 'not OK'):
Calls functionUnderTest(true) (returns a promise, but its result is discarded), The expression evaluates to the string 'not OK'.
Then await 'not OK' just resolves to 'not OK' immediately (not a promise).
console.assert('not OK');
Condition is 'not OK' (truthy), so the assertion passes regardless of what functionUnderTest actually does.
This does not meaningfully test the function and is misleading.
Option C:
console.assert(functionUnderTest(true), 'OK');
functionUnderTest(true) returns a Promise, not the string 'OK' directly.
A Promise object is always truthy.
So console.assert(promise, 'OK') will pass, even if the promise later rejects.
Also, there is no await, so we are not actually waiting for the async result.
This is not a correct way to assert on an async function's resolved value.
Option D:
console.assert(await functionUnderTest(true), 'not OK');
await functionUnderTest(true) still resolves to 'OK' (truthy).
console.assert('OK', 'not OK'); passes.
However, the message 'not OK' is the opposite of what we expect for the success case and is only used when the condition fails.
This makes the assertion logically inconsistent with the function behavior (it would show "not OK" if the assertion failed).
Therefore, the only assertion that:
Properly waits on the async function, and
Has expectation text that matches the successful behavior ('OK')
is:
Answe r: A
Study Guide / Concept Reference (no links):
async and await behavior in JavaScript
Promises resolving vs rejecting in async functions
console.assert(condition, message) usage
Truthy and falsy values in JavaScript
Comma operator (a, b) semantics
NEW QUESTION # 122
Refer to the code below:
Which replacement for the conditionalstatement on line 02 allows a developer to correctly determine that a specific element, myElement on the page had been clicked?
Answer:
Explanation:
event.target.id =='myElement'
NEW QUESTION # 123
Function to test:
01 const sum3 = (arr) => {
02 if (!arr.length) return 0;
03 if (arr.length === 1) return arr[0];
04 if (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 this function?
Answer: D,E
Explanation:
Length 1 → returns arr[0] → 0.
Assertion: 0 === 0 → true.
Also a correct and meaningful test.
Therefore, the valid and logically correct tests here are C and D.
Explanation:
Comprehensive and Detailed Explanation From Exact Extract JavaScript Knowledge:
Evaluate each test:
A). sum3([1, '2'])
Array length is 2 → line 4: arr[0] + arr[1] → 1 + '2' → '12' (string).
Assertion: '12' == 12 is true (type coercion).
However, this "test" is not logically correct: a numeric sum function should not be expected to return '12' as a string. It passes only because of weak equality coercion, so it is not a good/valid test of correct behavior.
B). sum3(['hello', 2, 3, 4])
Length ≥ 3 → line 5: 'hello' + 2 + 3 → 'hello2' + 3 → 'hello23'.
'hello23' === NaN is always false because NaN is never equal to anything, not even itself.
This assertion fails and also misunderstands how NaN comparisons work.
C). sum3([-3, 2])
Length 2 → -3 + 2 = -1.
Assertion: -1 === -1 → true.
This is a correct and meaningful test.
NEW QUESTION # 124
Given the code below:
What is logged to the console'
Answer: C
NEW QUESTION # 125
Refer to code below:
Let productSKU = '8675309' ;
A developer has a requirement to generate SKU numbers that are always 19 characters lon, starting with 'sku', and padded with zeros.
Which statement assigns the values sku0000000008675309 ?
Answer: B
NEW QUESTION # 126
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