Why Does String-to-Number Comparison Work in JavaScript?

Why String to Number Comparison Works in Javascript

In Javascript, you may encounter code that compares a string coming from an HTML text field with integers, like this:

x >= 1 && x <= 999;

This condition checks if the value x from the text field falls between 1 and 999 (inclusive), and it surprisingly works as expected. However, x is a string, while the condition involves integers. Shouldn't this lead to errors?

The Answer: Operator Coercion

Javascript defines operators like >= and <= to allow for coercion between different data types. Here's how it works:

• Both Operands as Strings: If both operands are strings, a string comparison is performed. For example, "90" > "100" because the comparison is based on character order rather than numeric value.
• One Operand as Non-String: If one of the operands is not a string, the operands are coerced to numbers. Thus, "90" < 100 because the former is coerced to the number 90 before the numeric comparison.

Implications

This coercion behavior can lead to unexpected results, such as:

"90" > "100" because strings are compared.
"90" < 100 because numbers are compared.

Should You Use parseInt()?