Understanding JavaScript's parseInt: Why Does It Print "5"?
Written on
Chapter 1: The Mystery of parseInt
Have you ever wondered why parseInt(0.0000005) in JavaScript outputs "5"? At first glance, this seems puzzling, as one might expect a result of 0. Let's delve into the reasoning behind this behavior together.
Section 1.1: When to Use parseInt
The parseInt function is primarily employed to convert strings into integers. To better understand its functionality, let’s examine how it operates in different scenarios.
Subsection 1.1.1: Understanding parseInt
According to the MDN documentation, the parseInt(string, radix) function takes a string as an argument and returns an integer based on the specified radix (base). Here’s how you might typically call this function:
parseInt(string)
parseInt(string, radix)
Examples:
parseInt('0.5') // 0
parseInt('0.05') // 0
parseInt('0.005') // 0
parseInt('0.0005') // 0
parseInt('0.00005') // 0
parseInt('0.000005') // 0
parseInt('015') // 15
parseInt('015', 8) // 13
parseInt('15px', 10) // 15
Section 1.2: The Mechanics of parseInt
How does parseInt handle numbers when the first argument is a numeric value? This is where the surprising output of parseInt(0.0000005) comes into play.
Step 1: String Conversion
When parseInt receives a number, it first converts it to a string. For instance:
String(0.5); // => '0.5'
String(0.0000005); // => '5e-7' (This is crucial!)
Step 2: Parsing the String
As discussed by SeyyedKhandon on Stack Overflow, parseInt(0.0000005) effectively evaluates to parseInt('5e-7'). The function only interprets the leading characters that resemble an integer, ignoring the remaining parts:
parseInt('5e-7') // 5
Thus, it returns 5 because that is the only valid integer character before the non-numeric 'e'.
Chapter 2: Safely Obtaining the Integer Part
To safely extract the integer portion of a floating-point number, consider using the Math.floor() function instead:
Math.floor(0.5); // => 0
Math.floor(0.0000005); // => 0
This method provides a more predictable output.
Curiosity Corner:
Can you explain why parseInt(99999999999999999999999999) returns 1?
In closing, I appreciate your time in exploring this topic with me, and I look forward to sharing more insightful articles in the future.