What is the Purpose of the Second Param in parseInt?

It is often overlooked or an unknown part of parseInt, but we have a second parameter that is responsible for the radix: The numeral system to be used. It can be an integer between 2 and 36. It is always a good practice to define the radix when using parseInt. Take the following as an example:

// This will return NaN
parseInt(2, 2);

// This will return 2
parseInt(2, 10);

If you simply want to convert a string into a number, you can also use the Number function more reliably, which doesn't require a radix:

Number('2'); // returns 2
Number(2);   // returns 2
Number('a'); // returns NaN

When the function is used on an invalid number, it will return NaN.

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Resources:

• The parseInt function in JavaScript
• The Number object