Mirendo,
var pattern = /^(\d+|\d+\.\d+)([+/*-])(\d+|\d+\.\d+)$/;
var matchValue = inputValue.match(pattern);
if (matchValue) {
var expression = matchValue[0];
var ltOperand = matchValue[1];
var operation = matchValue[2];
var rtOperand = matchValue[3];
}