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Html – How to use/process a math formula saved in JSON – in JavaScript

I am building a conversion calculator. I would like to store the references and formulas for the calculator in JSON.

I do not know how to "process the variable as math".

JSON

var JSON = {
  "conversions": [{[
 {
   "FromType": "in3",
   "ToType": "ft3",
   "Math": "/1728",
   "Description": "divide the volume value by 1728"
 }...

With the "Math" being done something like this.

D1 = document.getElementById("data1").value;
var theAnswer = eval(D1 conversions[0].Math);

Example:

D1 = 25
theAnswer = D1 /1728
theAnswer = 0.0144675

Is this possible? Is there a better way?

Tags:

2

Answers


  1. Chosen as BEST ANSWER
    0

    I had previously looked at Mathjs.. But, this is the route I went:

    Screen: enter image description here

    A Json Example:

    const JSON = {
  "conversions": [
  {
    "FromType": "atm",
    "ToType": "psi",
    "MathType": "multiply",
    "Factor": 14.696,
    "Description": "multiply the pressure value by 14.696"
  },
  {
    "FromType": "atm",
    "ToType": "mmHg",
    "MathType": "multiply",
    "Factor": 760,
    "Description": "multiply the pressure value by 760"
  }, ...

    Then I loop the Json to find the "FromType" and "ToType" based on what the user selects in a select drop down:

      function calcFormula(){
        
        
        convFrom = document.getElementById("ConvertA").value;
        convTo = document.getElementById("ConvertB").value;
        D1 = document.getElementById("data1").value;
        

let conversions = JSON.conversions;
       
  for (var i in conversions) {
    var FromType = conversions[i].FromType;
    var ToType = conversions[i].ToType;
    var MathType = conversions[i].MathType;
    var Factor = conversions[i].Factor;
    var Description = conversions[i].Description;
      
      
 
    if (FromType === convFrom && ToType === convTo ) {
     
        if (MathType === "multiply"){
            var theAnswer = (D1 * Factor);
            
        }else{
             var theAnswer = (D1 / Factor);
            
        }
        document.getElementById("convDescripton").innerHTML = Description;
    }
  }

    It is probably not as succinct as it could be, but it is working really well so far for conversions for mass, distance, pressure, etc...


  2. 0

    looks like you are trying to achieve while using eval() can work.

    I won’t recommend it because of security reasons. A better approach would be to use a safer method to process.

    Here is my suggestion:

    use a library like

    mathjs

    It is simple use the ‘mathjs’ library in the project, here is the path

    <script src="https://cdn.jsdelivr.net/npm/[email protected]/dist/math.min.js"></script>

    Then, we can use the library to evaluate math expressions.

    const math = require('mathjs');

// assume the conversion is your JSON object
const conversion = conversions[0];
const D1 = document.getElementById("data1").value;
const theAnswer = math.evaluate('{$D1} ${conversion.Math}');

console.log(theAnswer);
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