使用多个数字在JavaScript中拆分函数

Question

I'm having a little trouble understanding the split function in JavaScript.

I'm trying to get the numbers before and after the operator in a sum.

My code is as follows:

else if(btnVal == '=') {
            var equation = inputVal;
            var lastChar = equation[equation.length - 1];

            // Replace all instances of x with * respectively.
            equation = equation.replace(/x/g, '*');

            if (operators.indexOf(lastChar) > -1 || lastChar == ',')
               equation = equation.replace(/.$/, '');

            if (equation)
                if (equation.indexOf('+') == 1) {

                    var firstNumber = equation.split('+')[0];
                    var secondNumber = equation.split('+')[1];

                    var result = Number(firstNumber) + Number(secondNumber);

                    input.innerHTML = result;

                }
                else if (equation.indexOf('*') == 1) {
                    firstNumber = equation.split('*')[0];
                    secondNumber = equation.split('*')[1];

                    result = Number(firstNumber) * Number(secondNumber);

                    input.innerHTML = result;
                }
                else if (equation.indexOf('-') == 1) {
                    firstNumber = equation.split('-')[0];
                    secondNumber = equation.split('-')[1];

                    result = Number(firstNumber) - Number(secondNumber);

                    input.innerHTML = result;
                }
                else if (equation.indexOf('/') == 1) {
                    firstNumber = equation.split('/')[0];
                    secondNumber = equation.split('/')[1];

                    result = Number(firstNumber) / Number(secondNumber);

                    input.innerHTML = result;
                }

            decimalAdded = false;
        }

This all works just fine when I use 1 number, eg 1 + 1, but won't work with 77 + 8.

Could someone help me out on this one so that this also works with two numbers?

Answer 1

Below condition is wrong in case of input "77 + 1"

equation.indexOf('+') == 1

in above case indexOf '+' will be 2 instead of 1

change that line and for other operators as well like below

equation.indexOf('+') != -1