Question:
Write a Javascript program to get the extension of a filename.
Answer:
function fileNameExt (str) {
let extFileName = str.slice(str.lastIndexOf('.'));
return extFileName;
}
> declare a function 'fileNameExt'
> it has one parameter 'str'
> we declare a variable 'extFileName'
> it is initialized with a value when we use some basic string methods to get our output
> our program should extract the extension of a filename and return just that
>> like this: fileNameExt ('index.html') should return '.html'
> so first we use the slice function to slice the input and return the last portion of the string
> in order for the slice function to work, we need to pass in a start index number and an end index number (optional)
> since we do not know what the filename is, we cannot be sure of a specific index number
> the one thing we are sure of is that the extension name of a file is always followed by a dot
> however we do not know as to what type of file it is as it can have two dots as well
>> like this: webpack.config.js
> in the above example we have a file name that has two dots
> so we use the lastIndexOf method to find the last occurence of the dot in the filename
> we enter the lastIndexOf - 'dot' as the start number we want to pass, in the slice method
> this will slice our input string and return the entire portion following the last dot in a filename
> we then return the variable 'extFileName'
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