How Can I Validate and Convert Numeric Strings in JavaScript?

Determining the Validity of Numerical Strings

When dealing with data in programming, verifying the validity of numeric input is often crucial. JavaScript offers various approaches to accomplish this task.

1. Checking if a Variable is a Number

To determine if a variable, including strings, represents a valid number, utilize the isNaN() function:

isNaN(num); // Returns true if the variable does not contain a valid number

Examples:

isNaN(123); // false
isNaN('123'); // false
isNaN('foo'); // true
isNaN(''); // false

2. Converting Strings to Numbers

To convert a string containing a number into a numeric value, use the num syntax:

+num; // Returns the numeric value of the string, or NaN if it is not purely numeric

Examples:

+'12'; // 12
+'foo'; // NaN
+'12px'; // NaN

3. Converting Strings Loosely to Numbers

For situations where the string may contain non-numeric characters, parseInt() can be useful:

parseInt(num); // Extracts a numeric value from the start of the string, or NaN

Examples:

parseInt('12px'); // 12
parseInt('foo2'); // NaN

Note: parseInt() treats floats as integers, truncating the decimal portion.

4. Handling Empty Strings

Empty strings in JavaScript exhibit unique behavior with numeric conversion functions:

+''; // 0
isNaN(''); // false
parseInt(''); // NaN

Conclusion

Choosing the appropriate method for validating and converting numeric strings in JavaScript depends on the specific requirements and context of the application.

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