Can JSON strings be converted to fractions for equations when building REST API in Node JS?-CodePudding

I am creating an API for a picture framing calculator. I am using Node JS with Express. The code that I'm using is this:

        app.post("/api/calculator/singlematapi", (req,res) => {
        
        let FrameWidth = req.body.FrameWidth;
        let FrameWidthFraction = req.body.FrameWidthFraction
        let FrameHeight = req.body.FrameHeight;
        let FrameHeightFraction = req.body.FrameHeightFraction;
        let PictureWidth = req.body.PictureWidth;
        let PictureWidthFraction = req.body.PictureWidthFraction;
        let PictureHeight = req.body.PictureHeight;
        let PictureHeightFraction = req.body.PictureHeightFraction;
        let MatOverlap = req.body.MatOverlap;
        let MatOverlapFraction = req.body.MatOverlapFraction
        let width = (1/2)*((FrameHeight FrameHeightFraction)-(PictureHeight PictureHeightFraction) (MatOverlap MatOverlapFraction));
        let height = (1/2)*((FrameWidth FrameWidthFraction)-(PictureWidth PictureWidthFraction) (MatOverlap MatOverlapFraction));
        res.send(`Width Cut = ${new Fraction(width).toString()}", Height Cut = ${new Fraction(height).toString()}"`);
    });

Therefore, a JSON POST request would be:

{
    "FrameWidth": 16,
    "FrameWidthFraction": 0,
    "FrameHeight": 20,
    "FrameHeightFraction": 0,
    "PictureWidth": 11,
    "PictureWidthFraction": 0,
    "PictureHeight": 17,
    "PictureHeightFraction": 0,
    "MatOverlap": 0.5
}

What I am trying to accomplish is that instead of a decimal - a fraction such as 1/2 can be inputted instead. For example:

{
    "FrameWidth": 16,
    "FrameWidthFraction": 0,
    "FrameHeight": 20,
    "FrameHeightFraction": 0,
    "PictureWidth": 11,
    "PictureWidthFraction": 0,
    "PictureHeight": 17,
    "PictureHeightFraction": 0,
    "MatOverlap": 1/2
}

The problem I'm running into is that although I am able to convert the output from decimal to fraction using a library and this piece of code:

res.send(`Width Cut = ${new Fraction(width).toString()}", Height Cut = ${new Fraction(height).toString()}"`);

...I am not able to use a fraction as an input instead of a decimal.

Unless I'm misunderstanding - it states here: JSON data types - that Fractions pertaining to Numbers can only be displayed in decimal type formatting such as 0.5 like I have above under MatOverlap.

However, according to the same page it states that a forward slash can be used in a string.

Can I use the forward slash as the solidus to indicate a fraction when JSON data is inputted?

When I attempted to use a string by changing the above to:

{
   "MatOverlap": "1/2"
}

...then it throws NaN error.

CodePudding user response：

You can convert string expression to number using eval. Yes yes. But first sanitize it because it's a dangerous command to run on input.

var req = {
  body: {
    MatOverlap: "1/2"
  }
}

let expr = req.body.MatOverlap;  
expr = expr.replace(/[^0-9//]/g, "");

let MatOverlap = eval(expr);
console.log(MatOverlap * 6)

CodePudding user response：

you can convert the fraction input to decimal.

let MatOverlap = req.body.MatOverlap.split("/").reduce((a, b) => a / b)