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JavaScript Interview Questions - Page 4

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Question: What is the purpose of the 'map()' function and how does it differ from 'forEach()' loop?
Answer: The 'map()' function is used to iterate over an array and apply a transformation or operation to each element, creating a new array with the results of these operations.

While both 'map()' and 'forEach()' iterate over each element in an array, the 'map()' function returns a new array containing the results of applying a provided function to each element, while 'forEach()' simply executes a provided function for each array element without returning anything.

Question: Can you explain the syntax of the map() function in JavaScript?
Answer: The syntax of the 'map()' function is as follows:
 array.map(callback(currentValue, index, array), thisArg)
callback: Function to execute on each element of the array.
currentValue: The current element being processed in the array.
index (optional): The index of the current element being processed.
array (optional): The array that map() is being applied to.
thisArg (optional): Value to use as this when executing the callback function. •

Question: What is the purpose of the 'reduce()' function in JavaScript and how is it used?
Answer: The 'reduce()' function is used to reduce an array to a single value, applying a provided function to each element of the array and accumulating the result. It is used like below:
 array.reduce(callback(accumulator, currentValue, index, array), initialValue)
callback: Function to execute on each element of the array, taking four arguments: accumulator, currentValue, index, and array.
accumulator: The accumulated value returned in last invocation of callback, or initialValue if provided - otherwise first array element is used.
currentValue: The current element being processed in the array.
index (optional): The index of the current element being processed.
array (optional): The array that reduce() is being applied to.
initialValue (optional): Initial value to use as the first argument to the first call of the callback.

Question: What are jQuery plugins, and how do you use them?
Answer: jQuery plugins are pieces of code that extend the functionality of jQuery by adding new methods or features. They are often provided as external JavaScript files that you include in your HTML document after including jQuery.
Question: How do you make an AJAX request with jQuery?
Answer: One can make AJAX requests with jQuery using the '$.ajax()' function or the shorthand methods like '$.get()', '$.post()', '$.getJSON()', etc. These methods allow one to asynchronously fetch data from a server without reloading the page.

Question: How do you create custom animations in jQuery?
Answer: One can create custom animations in jQuery using the '.animate()' method. This method allows one to specify CSS properties to animate, the duration of the animation, easing effects, and a callback function to execute when the animation completes.


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