If you’re building a calculator application using JavaScript, and you want to evaluate operations (+, -, *, /) based on user input, how would you structure a switch statement to handle this?
- Create separate case statements for each operation (+, -, *, /) and perform the corresponding calculation within each case.
- Use regular expressions to match the input against valid operations and handle them accordingly in a single case.
- Convert the user input into a numerical expression and evaluate it within the switch statement.
- Use an if-else statement to check for each operation and perform the corresponding calculation.
To handle different mathematical operations (+, -, *, /) based on user input in a calculator application, it's best to create separate case statements for each operation within a switch statement. This approach is clear and maintainable, allowing you to perform the corresponding calculation for each operation. Using regular expressions within a single case or converting the input into a numerical expression unnecessarily complicates the code. An if-else statement is less idiomatic and less efficient for this purpose.
How does the "this" keyword behave in event handlers?
- It refers to the element that triggered the event.
- It refers to the document object.
- It always refers to the window object.
- It throws an error since "this" cannot be used in event handlers.
In event handlers, such as those in JavaScript for the web, the "this" keyword typically refers to the DOM element that triggered the event. This behavior allows developers to access and manipulate the specific element that triggered the event, making it a powerful feature in front-end web development.
Which method can be used to insert an HTML element as the first child of a parent element?
- appendChild()
- insertBefore()
- prepend()
- createElement()
To insert an HTML element as the first child of a parent element, you should use the prepend() method. This method adds the element as the first child, making it the top element within the parent. appendChild() adds it as the last child. insertBefore() requires specifying a reference node. createElement() creates an element but doesn't insert it.
What is the purpose of the capture parameter in addEventListener method?
- To specify the event phase
- To control event order
- To attach multiple listeners simultaneously
- To prevent event propagation during capture phase
The capture parameter in the addEventListener method is used to specify the event phase during which the listener should be triggered. When set to true, the listener is triggered during the capturing phase, and when set to false, it is triggered during the bubbling phase. This parameter helps control the order of event execution.
To strictly compare the inequality of two operands without type coercion, use _______.
- ==
- ===
- !=
- !==
To strictly compare the inequality of two operands without type coercion in JavaScript, you should use the === operator. This operator checks both the value and the data type of the operands. In contrast, the == operator performs type coercion and may not provide the desired strict comparison.
What is the purpose of the innerHTML property in JavaScript?
- To access the element's content
- To set the element's ID
- To toggle element visibility
- To retrieve the element's tag name
The innerHTML property in JavaScript is used to access the content of an HTML element. It allows you to retrieve or modify the HTML content within the element, including any child elements, text, or HTML tags.
In JavaScript, the arithmetic operator _______ is used to exponentiate a number.
- **
- ^
- exp
- pow
In JavaScript, the ** operator is used to exponentiate a number. For example, 2 ** 3 evaluates to 8, as it calculates 2 raised to the power of 3. This operator was introduced in ECMAScript 2016 (ES6) to provide a concise way of performing exponentiation.
What method can be used to select the first
element inside a
?
- div.getElementsByTagName('p')[0]
- div.querySelector('p:first-child')
- div.querySelector('p')
- div.getElementByTagName('p')
You can use div.querySelector('p') to select the first
element inside a
. This method finds the first
element that is a descendant of div. Alternatively, you can use getElementsByTagName('p')[0], but querySelector is more flexible and widely used.
Which keyword is used to create a class in JavaScript?
- class
- new
- function
- prototype
In JavaScript, the class keyword is used to create a class. Classes provide a convenient and more structured way to define constructor functions and prototypes. While new is important for instantiating objects, it's not used to create classes. The function and prototype keywords are used in traditional constructor-based object creation.
How can you modify the behavior of for...of loops with iterables?
- By using the for...in loop instead.
- By providing a custom iterator object.
- By using Array.prototype.forEach() method.
- By changing the loop syntax (e.g., for...to).
You can modify the behavior of for...of loops with iterables by providing a custom iterator object. Iterables in JavaScript have an @@iterator method that defines how the iteration should behave. By implementing this method, you can customize how for...of iterates over your objects.
How can a "for" loop be used for asynchronous operations efficiently?
- By using "await" within the loop body
- By using a "setTimeout" function inside the loop
- By using "return" statements in the loop
- By using "if...else" conditions in the loop
To use a "for" loop for asynchronous operations, you can use the "await" keyword within the loop body, making it an "async" function. This allows you to wait for asynchronous tasks to complete in each iteration, ensuring that the loop proceeds in an orderly fashion. The other options are not suitable for efficient asynchronous operations.
What is NOT a consequence of dynamic scoping, considering JavaScript uses lexical scoping?
- Variables can change unexpectedly
- Function definitions capture their context
- Easier to reason about
- Potential bugs due to unexpected changes
In JavaScript, dynamic scoping is not a consequence since JavaScript primarily uses lexical scoping. With lexical scoping, variable scope is determined by the placement of variables in the source code, making it easier to reason about the code's behavior. Dynamic scoping, where scope is determined by the calling context at runtime, can lead to unexpected changes in variable values and potential bugs, but it is not a consequence of JavaScript's lexical scoping.