currency-validator.js

var currencyValidator = {
		format: function (number, floats = 2) {
			return (Math.trunc(number * 100) / 100).toFixed(floats)
		},
		parse : function (newString, oldNumber) {
			
			var CleanParse = function (value) {
				return {value: value}
			};
			
			var CurrencyWarning = function (warning, value) {
				return {
					warning: warning,
					value  : value,
					attempt: newString
				}
			};
			
			var NotAValidAmountWarning = function (value) {
				return new CurrencyWarning(newString + ' is not a valid  amount', value)
			};
			
			var AutomaticConversionWarning = function (value) {
				return new CurrencyWarning(newString + ' was automatically converted to ' + value, value)
			};
			
			var newNumber  = Number(newString);
			var indexOfDot = newString.indexOf('.');
			var indexOfE   = newString.indexOf('e');
			
			if (isNaN(newNumber)) {
				if (
					indexOfDot === -1 &&
					indexOfE > 0 &&
					indexOfE === newString.length - 1 &&
					Number(newString.slice(0, indexOfE)) !== 0
				) {
					return new CleanParse(oldNumber)
				} else {
					return new NotAValidAmountWarning(oldNumber)
				}
			}
			
			var newCurrencyString = currencyValidator.format(newNumber);
			var newCurrencyNumber = Number(newCurrencyString);
			
			if (newCurrencyNumber === newNumber) {
				if (indexOfE !== -1 && indexOfE === newString.length - 2) {
					return new AutomaticConversionWarning(newNumber)
				} else {
					return new CleanParse(newNumber)
				}
			} else {
				return new NotAValidAmountWarning(
					newNumber > newCurrencyNumber
						? newCurrencyNumber
						: oldNumber
				)
			}
		}
	};