JavaScript | Date.parse()

The date.parse() method in JavaScript converts a string containing a date to a numeric value by representing that date in the form of milliseconds since 1970. The working of the parse() is the same as passing a string as an argument to the constructor of the Date variable class. Well, in reality, when a string is passed as an argument, an indirect call is made to the date parse() method.

Syntax of date.parse()

The syntax of the date parse() method is rather simple; it is defined as


Note: Here, the String contains a date value inside it. Now, the user can give this representation in various formats.

Return Value:

The return value from the date parse() method is a numeric value that represents the amount of time elapsed in the form of milliseconds since January 1st, 1970. A NaN is returned as the outcome if the argument equals an invalid date.

Example 1: Passing a string in the parse() method

For this example, create a new string variable, and write a valid date inside that variable like

dateInString = "5 June 1997";

Then, pass this variable in the argument of the parse() method and set it equal to a new variable dateInMs:

const dateInMs = Date.parse(dateInString);

Finally, print out the result stored inside the dateInMs variable onto the terminal using the console log function:


These lines are going to yield the following outcome when executed:

From the screenshot, observe that the output is a numeric value representing time in the form of milliseconds.

Example 2: Calculating the Years from the result of the parse() method

Create a new string with the following value inside it:

dateInString = "1 Jan 2010";

Pass it to the Date.parse() method and then print the result onto the console using the console log function:

const dateInMs = Date.parse(dateInString);


Since, the result is going to be the amount of time elapsed since January 1st, 1970. We can calculate the years passed since 1970 using the following lines:

var yearsPassed = Math.round(dateInMs / (365 * 24 * 60 * 60 * 1000));


The equation (365*24*60*60*1000) is simply calculating the number of milliseconds inside a whole year. After that, divide the result of the parse() method by that number and then display it onto the console using the console log function:

The years passed since 1970 were printed onto the terminal.

Example: Passing Invalid Date to Date.parse() method

To demonstrate this, create a new string containing an invalid date as

dateInString = "31 2 2022";

The date represented by this string is the 31st of February, 2022, which is an invalid date. Pass this dateInString variable in the argument of the parse() method and pass the result to the console log function as

const dateInMs = Date.parse(dateInString);


After executing this program, the following result would be displayed onto the terminal:

The result was NaN meaning depicting that the string contained an invalid date.


The Date.parse() method simply takes a string representing a specific date. Afterward, it returns the number of milliseconds elapsed since January 1970 according to the date in the string. In case there are wrong \ invalid dates in the string, the result would be a NaN value. Besides, whenever a new Date variable is created using the new Date() constructor, an indirect call is made to the Date.parse() method.

About the author

Abdul Mannan

I am curious about technology and writing and exploring it is my passion. I am interested in learning new skills and improving my knowledge and I hold a bachelor's degree in computer science.