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# Adding a Leading Zero in 1 Line in JavaScript

At work, I recently ran into a scenario where we were capturing a user's date of birth (DOB). This information is collected in 3 fields day, month, and year. If your DOB is January 7, 1962, people were inputting 1 for the month, 7 for the day, and 1962 for the year. This sounds good but our back-end database required both the month and day to be 2 digits. So I needed to find a way to add a leading zero for both of these fields.

## Starting Data

``````let month = 1;
let day = 7;``````

My simple solution in one line is:

``month = `0\${month}`.slice(-2)``

Let's walk through this code. This combines `0` with the value the user inputs for their month. Then it takes the right two digits and assigns this to the month.

But what if the user inputs the value `10` for their month? It still works. It will combine 0 with 10 to produce `010` and then it takes the right two digits which is `10`.

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I am a Google Developers Expert. Entrepreneur. Mountain Climber. Neil Diamond fanatic. World traveler. MBA grad. Software Engineer. Interested in hiring me? Contact me at ratracegrad@gmail.com

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