Javascript code - code check
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I'm new to Javascript and trying to learn some basics.

Can you please check if I had done the following correctly? If not, please outline what I've yet to do.

I had to:

•	Calculate the user's month of birth as a number where January=0 through to December=11.
•	Take the string entered
•	Get the substring being the first three characters
•	Convert to uppercase
•	Find the starting location of the three letter abbreviation in the month abbreviations string
•	Divide this by 3
•	(This is not the only way to find the month number, but it allows us to practice searching in a string)


My code:

        var year = prompt('Enter year of birth as a 4 digit integer');  

        var month = prompt('Enter the name of the month of birth');
	// Chop everything after the first 3 characters and make it lowercase
	month = month.substr(0,3).toLowerCase();
	// Store your array in months, differently named than the month input
	var months = ["jan", "feb", "mar", "apr", "may", "jun", "jul", "aug", "sep", "oct",
    "nov", "dec"];  

    // We then use array.indexOf() to locate it in the array
	var pos = months.indexOf(month);
	if (pos >= 0) {
    // valid month, number is pos
    }