How to avoid eval for string to decimal conversion

I have "1/7" and开发者_如何学运维 want to get decimal equivalent. Ofcourse I can use eval( "1/7"), but considering eval is evil, any other method?

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eval is not evil. It's only evil to use it on arbitrary strings without checking your input.

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You can write your own function, it's not really complicated and pretty efficient:

function ParseFloat(sFloat) {
    var parts = sFloat.split("/");
    if (parts.length == 2) {
        var first = parseInt(parts[0], 10);
        var second = parseInt(parts[1], 10);
        if (!isNaN(first) && !isNaN(second))
            return first / second;
    }
    return NaN;
}

Usage:

var s = "1/7";
alert(ParseFloat(s));

Live test case: http://jsfiddle.net/RK3zS/

Edit: if you're after working with such entities, I would use "class" for this for example:

function DecimalFraction(first, second) {
    this.first = first;
    this.second = second;
    this.toString = function() {
        return first / second;
    }
}

And then:

var s = new DecimalFraction(3, 7);
alert(s);

More elegant in my opinion. Updated jsFiddle.

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That's the only option we have, I guess. Eval is not that evil too. Else create own function to identify values and do calculations.

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Assuming you have to calculate decimals and only decimals:

txt = "1/7";

firstNumber = txt.subString(0, txt.indexOf('/'));
secondNumber = txt.subString(txt.indexOf('/') + 1, txt.length);

decml = fistNumber / secondNumber;

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try it like this.

var txt = "1/7";
var result = new Function("return " + txt)()
console.log(result); // 0.14285714285714285