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

Is There an Equivalent to VB6's IsNumeric() Function in JavaScript?

JavaScript offers analogous functions for checking if a string represents a valid number.

Using isNaN() to Validate Numeric Inputs:

For a comprehensive approach, use isNaN(), which returns true if the variable (whether it's a string or number) is not a valid number. This method effectively handles various scenarios:

isNaN(123);         // false
isNaN('123');       // false
isNaN('1e10000');   // false (Infinity, considered a number)
isNaN('foo');       // true
isNaN('10px');      // true
isNaN('');          // false
isNaN(' ');         // false

You can easily invert this check for an equivalent to IsNumeric():

function isNumeric(num) {
  return !isNaN(num);
}

Converting Strings to Numbers:

To transform a numeric string into a number:

+num;               // returns the numeric value or NaN

Examples:

+'12';              // 12
+'12.';             // 12
+'12..';            // NaN
+'.12';             // 0.12
+'..12';            // NaN
+'foo';             // NaN
+'12px';            // NaN

Loose Conversion with parseInt()

This function extracts the initial numeric value from a string, ignoring any trailing non-numeric characters:

parseInt(num);      // returns the numeric value or NaN

Examples:

parseInt('12');     // 12
parseInt('aaa');    // NaN
parseInt('12px');   // 12
parseInt('foo2');   // NaN
parseInt('12a5');   // 12
parseInt('0x10');   // 16

Handling Floats and Empty Strings

Note that parseInt() converts floats to integers, while num preserves decimal values. Empty strings are converted to zero by num but result in NaN when using parseInt().

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