Is There a JavaScript Equivalent to VB6's IsNumeric Function?

Checking String for Numeric Value

Question:

Exists there a function similar to VB6's IsNumeric() function that checks if a given string represents a valid numeric value?

Answer:

Robust Implementation for Whitespace and Radix Handling:

function isNumeric(str) {
  if (typeof str != "string") return false; // Only process strings
  return !isNaN(str) && !isNaN(parseFloat(str));
}

Verification Using isNaN():

To determine if a string (or variable) contains a valid number, utilize the isNaN() function:

isNaN(num); // Returns true if the value is not a number

Converting String to Number:

For strings containing exclusively numeric characters, the operator converts them to numbers:

+num; // Numeric value or NaN if string is not purely numeric

Loose String-to-Number Conversion:

To extract numeric values from strings containing non-numeric characters, use parseInt():

parseInt(num); // Numeric value or NaN if string starts with non-numeric characters

Floats and Integers:

Note that parseInt() truncates floats to integers, unlike num:

+'12.345'; // 12.345
parseInt(12.345); // 12
parseInt('12.345'); // 12

Empty Strings:

num and isNaN() treat empty strings as zero, while parseInt() considers them as NaN:

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

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