Simple calculator example using array to store input values

Question

The input values are stored in an array, the below loop is to calculate the final result, by looping through the array and appending the operators and numbers to a variable which is then evaluated.

privateCalculate = function () {
    var total;

    for(i = 0; i < init.sequence.length; i++) {
        if(init.sequence[i] === "+" || init.sequence[i] === "-" ||
           init.sequence[i] === "*" || init.sequence[i] === "/" ||
           init.sequence[i] === "(" || init.sequence[i] === ")") 
        {
            total += init.sequence[i];
        } else {
            init.sequence[i] = parseFloat(init.sequence[i]);

            total += init.sequence[i];
        }

    }

    console.log(eval(total));
    //console.log((parseFloat(1)+parseFloat(2))/parseFloat(2));
},

The function produces "NaN"

["5", "+", "5"], the if logic is intended to convert "5" to 5 — Conor
– Conor, Commented Nov 23, 2015 at 23:45
Drop the parseFloat, your strings will be converted to ints with eval anyway — JCOC611
– JCOC611, Commented Nov 23, 2015 at 23:53
the numbers are being converted back to strings anyway, so this makes no sense. just join the values total=init.sequence.join("") — Shanimal
– Shanimal, Commented Nov 23, 2015 at 23:56
What??? Sorry but if you have var arr = ["10","+","5","-","2","*","3"] >>> this is all you need: eval(arr.join("")) — Roko C. Buljan
– Roko C. Buljan, Commented Nov 23, 2015 at 23:57

webdeb · Accepted Answer · 2015-11-23 23:58:46Z

1

You said your input is: ["5","+","5"] You don't need to parse it, because evaltakes as parameter a String

Just do this:

var inputArray = ["5","+","5"];
eval(inputArray.join('')) // -> 10

answered Nov 23, 2015 at 23:58

webdeb

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3 Comments

Roko C. Buljan Over a year ago

Yes. Exactly what I said in comments. Though be careful not to allow global access to the eval or trough function arguments/ callbacks etc. In that case it could be exploited to attacks.

webdeb Over a year ago

@RokoC.Buljan two dumb guys, one though :)

Roko C. Buljan Over a year ago

Yes, eval is a "feature" unless you knew it :D

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