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| Section | Weight | Objectives |
|---|---|---|
| Topic 1: Asynchronous Programming | 13% | - Event loop and execution flow - Asynchronous patterns for business requirements - Callbacks - Async/Await syntax - Promises (creation, chaining, error handling) |
| Topic 2: Testing | 7% | - Writing and modifying unit tests - Unit testing concepts - Test coverage and reliability - Test effectiveness evaluation |
| Topic 3: Server Side JavaScript | 8% | - Package management (npm) - CLI commands - Core Node.js modules - Server-side JavaScript implementations - Node.js fundamentals |
| Topic 4: Variables, Types, and Collections | 23% | - Type coercion and conversion - Variable declarations and initialization - Arrays and collections - JSON parsing and manipulation - Strings, numbers, and dates - Truthy and falsy evaluations - Primitive and complex data types |
| Topic 5: Objects, Functions, and Classes | 25% | - Prototypal inheritance - Modules and decorators - Execution flow and context - ES6 classes and inheritance - Object creation and manipulation - Function declarations and expressions - Higher-order functions - Variable scope and closures - Arrow functions |
| Topic 6: Debugging and Error Handling | 7% | - Error handling techniques (try/catch/finally) - Custom error types - Console methods for debugging - Breakpoints and code inspection |
| Topic 7: Browser and Events | 17% | - Event propagation (bubbling and capturing) - Browser-specific APIs - Event handling and listeners - Interacting with forms and user input - DOM manipulation - Browser Developer Tools usage |
>> JavaScript-Developer-I Test Topics Pdf <<
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NEW QUESTION # 74
A developer receives a comment from the Tech Lead that the code given below has error:
const monthName = 'July';
const year = 2019;
if(year === 2019) {
monthName = 'June';
}
Which line edit should be made to make this code run?
Answer: B
NEW QUESTION # 75
Refer to the following array:
Let arr1 = [ 1, 2, 3, 4, 5 ];
Which two lines of code result in a second array, arr2 being created such that arr2 is not a reference to arr1?
Answer: B,D
NEW QUESTION # 76
A developer wrote the following code to test a sum3 function that takes in an array of numbers and returns the sum of the first three numbers in the array. The test passes:
01 let res = sum3([1, 2, 3]);
02 console.assert(res === 6);
03
04 res = sum3([1, 2, 3, 4]);
05 console.assert(res === 6);
A different developer made changes to the behavior of sum3 to instead sum all of the numbers present in the array.
Which two results occur when running the test on the updated sum3 function?
Answer: B,C
Explanation:
New behavior: sum3 now returns the sum of all elements .
* Line 01: sum3([1, 2, 3]) # 1 + 2 + 3 = 6
* Assertion on line 02: res === 6 # passes.
* Line 04: sum3([1, 2, 3, 4]) # 1 + 2 + 3 + 4 = 10
* Assertion on line 05: res === 6 # 10 === 6 is false, so the assertion fails.
So:
* Line 02 assertion passes # D.
* Line 05 assertion fails # C.
NEW QUESTION # 77
Refer to the code below:
let inArray = [ [1, 2], [3, 4, 5] ];
Which two statements result in the array [1, 2, 3, 4, 5]?
(With corrected typing errors: usArray # inArray, .. # ....)
Answer: C,D
Explanation:
We start with the array:
let inArray = [ [1, 2], [3, 4, 5] ];
This is an array of two inner arrays:
* First element: [1, 2]
* Second element: [3, 4, 5]
The desired result is to transform this into a single, flat array:
[1, 2, 3, 4, 5]
This is accomplished by using Array.prototype.concat to concatenate the inner arrays into one new array, optionally combined with the spread syntax (...) or Function.prototype.apply.
* Option A: [].concat(...inArray);
Relevant concepts:
* Spread syntax (...inArray) expands an iterable into separate arguments.
* Array.prototype.concat joins arrays or values into a new array. When you pass arrays as arguments to concat, it flattens them one level into the result.
Step-by-step behavior:
* inArray is [ [1, 2], [3, 4, 5] ].
* ...inArray expands into [1, 2] and [3, 4, 5] as separate arguments.
* So [].concat(...inArray) is equivalent to:
* [].concat([1, 2] , [3, 4, 5]);
* concat processes each argument:
* For [1, 2], it adds 1 and 2 into the result array.
* For [3, 4, 5], it adds 3, 4, and 5 into the result array.
The final outcome is:
[1, 2, 3, 4, 5]
Therefore, Option A correctly produces the desired array.
* Option B: [].concat.apply(inArray, [] );
Corrected name from usArray to inArray.
Relevant concepts:
* Function.prototype.apply(fnThis, argsArray) invokes a function with a specific this value and a list of arguments passed as an array.
Here:
* thisArg is inArray.
* argsArray is [] (no actual arguments passed).
So the call:
[].concat.apply(inArray, [] );
is equivalent to:
Array.prototype.concat.apply(inArray, []);
// i.e. inArray.concat();
Since there are no extra arguments, inArray.concat() simply returns a shallow copy of inArray:
[ [1, 2], [3, 4, 5] ]
This remains an array of arrays and is not flattened into [1, 2, 3, 4, 5]. Therefore, Option B does not produce the required result.
* Option C: [].concat::...inArray();
Corrected name from usArray to inArray and .. to ....
This expression uses syntax that is not part of standard JavaScript:
* :: (double colon) was proposed in early drafts as a bind operator but is not part of the official ECMAScript standard.
* The combination concat::...inArray() is invalid in normal JavaScript engines and cannot be used as a valid way to flatten arrays.
* In addition, inArray() would imply calling inArray as a function, but it is an array, which would cause a runtime error.
Hence, Option C is syntactically or semantically invalid in standard JavaScript and does not provide the required result [1, 2, 3, 4, 5].
* Option D: [].concat.apply({}, inArray);
Corrected name from usArray to inArray.
Relevant concepts:
* Again, Function.prototype.apply is used to call concat with a specific this value and arguments provided as an array.
* concat treats its this value as an array-like object but ultimately returns a new array containing concatenated elements.
In this expression:
[].concat.apply({}, inArray);
* thisArg is {} (an empty object).
* argsArray is inArray, which is [ [1, 2], [3, 4, 5] ].
Using apply, this is interpreted as calling concat like:
Array.prototype.concat.call({}, [1, 2], [3, 4, 5] );
concat then:
* Starts from the array-like this (here {} is treated as an empty base).
* Takes the first argument [1, 2] and appends its elements 1 and 2 to the result.
* Takes the second argument [3, 4, 5] and appends its elements 3, 4, and 5 to the result.
The resulting new array is:
[1, 2, 3, 4, 5]
Therefore, Option D also correctly produces the required array.
* Final evaluation of all options:
* Option A: Uses spread syntax with concat and correctly flattens one level: [1, 2, 3, 4, 5].
* Option B: Equivalent to inArray.concat(), leaving it as [[1, 2], [3, 4, 5]] . Does not flatten the structure.
* Option C: Uses non-standard and invalid syntax; not a valid or correct JavaScript solution.
* Option D: Uses apply with concat, passing the inner arrays as arguments and flattening one level to [1,
2, 3, 4, 5].
Thus, the two correct statements are:
The answer: A, D
References of JavaScript knowledge documents or Study Guide (concept names only):
* Array.prototype.concat (concatenating and one-level flattening behavior)
* Spread syntax for arrays (...array)
* Function.prototype.apply (calling a function with a given this value and arguments list)
* Array flattening by one level using concat with array arguments
* Distinction between nested arrays and flat arrays in JavaScript
NEW QUESTION # 78
is below:
<input type="file" onchange="previewFile()">
<img src="" height="200" alt="Image Preview..."/>
The JavaScript portion is:
01 function previewFile(){
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?
Answer: B
NEW QUESTION # 79
......
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