parse-number.js

/** 
 *  Returns a number from a given string. It ignores any characters, including
 *  comma's and points. When more than 1 number is found in a string, the last
 *  number is used as the fractional of the number. For example:
 *
 *      '€ 12,34' => 12.34
 *      '1,234.567 %' => 1234.567
 * 
 *  @argument {string} text - text containing the number or number parts
 *  @returns {number|undefined} - parsed number or undefined when none found
 */
function parseNumber(text) {
    var pattern = /\d+/gmi;
    
    var numberParts = text.match(pattern) || [];
    
    if (numberParts.length === 0) {
    	return undefined;
    } else if (numberParts.length === 1) {
        // add fractionals if numberParts only contains 1 number
        numberParts.push('0');
    }
    
    var integers = Number.parseInt(numberParts.slice(0, -1).join(''));
    var fractionals = Number.parseInt(numberParts.slice(-1)[0]);
    
    return integers +
        (fractionals / (Math.pow(10, fractionals.toString().length)));

}

console.clear();

var tests = [
    { in: '€ 12', out: 12 },
    { in: '€ 12,47', out: 12.47 },
    { in: '€ 12,00', out: 12 },
    { in: '€ 12,345', out: 12.345 },
    { in: '€ 0,35', out: 0.35 },
    { in: '€ 1.234,56', out: 1234.56 },
    { in: '€ 1.234.567,89', out: 1234567.89 },
    { in: '12', out: 12 },
    { in: '$ 12.47', out: 12.47 },
    { in: '$ 12.00', out: 12 },
    { in: '$ 0.35', out: 0.35 },
    { in: '$ 1,234.56', out: 1234.56 },
    { in: '$ 1,234,567.89', out: 1234567.89 },
    { in: '', out: undefined },
    { in: 's', out: undefined },
];

tests.forEach(function(test) {
    var result = parseNumber(test.in);
    console.log(result === test.out ? 'success' : 'fail');
});