Substituting variable value in string for a function call

Question

I'm a newbie so forgive me if my terminology doesn't make sense. Here goes....

If I have the following variables in JS:

var LE_TotalAnnualIncome = "50000";
var LE_TypeOfSP = "Single";
var LE_NoDependants = "1";
var LE_Customer = "3000";

How can I convert the string:

MinimumLivingExpenses(LE_TotalAnnualIncome,LE_TypeOfSP,LE_NoDependants,LE_Customer)

To:

MinimumLivingExpenses("50000","Single","1","3000")

Edited to add this: This code might explain what I'm trying to achieve:

function Calculate()
{
var elements = frm_livingexpenses.elements;
var el;
var reClass = /(^|\s)inputCalculated(\s|$)/;

// Searches for fields that need to be calculated
for (var i=0, iLen=elements.length; i<iLen; i++) 
{
    el = elements[i];
    if (reClass.test(el.className))
    {
        // if contents of element are a formula, calculate result
        // the element will have an '=' if it's a formula
        var GetFormula = document.getElementById(elements[i].name).getAttribute('data-formula');
        if (GetFormula.substring(0,1) == '=')
        {
            elements[i].value = eval(GetFormula.substring(1,999));
            eval(elements[i].name.substring(12,999) + '="' + elements[i].value + '";');
            // this is where the variables are set. eg
            // var LE_TotalAnnualIncome = "50000";
            // var LE_TypeOfSP = "Single";
            // var LE_NoDependants = "1";
            // var LE_Customer = "3000";
        }

        // if contents of element are a function call, send to function
        // the element will have a '#' at the front if I need to call a function
        if (GetFormula.substring(0,1) == '#')
        {
        // eg. #MinimumLivingExpenses(LE_TotalAnnualIncome,LE_TypeOfSP,LE_NoDependants,LE_Custo‌​mer)
        // this should be:  MinimumLivingExpenses("50000","Single","1","3000")
        alert('Ajax call will use this in URL='+GetFormula.substring(1,999));
        }
    }
}

}`

Answer 1

One way to achieve what you want is creating an object to store the variables. Notice the added benefit of not evaling anything. In order to do it:

• Define the object:

  var reClass = /(^|\s)inputCalculated(\s|$)/;
  var variables = {};
  

• Add the variables as properties using bracket notation - just change your eval() to this:

  // Empty string concatenation to make sure the value stored is cast to string
  variables[elements[i].name.substring(12,999)] = '' + elements[i].value;
  

• Construct the string by getting values from the object. Notice that I create a new list of variables, instead of simply going through all properties of the object. The reason is that looping through object properties doesn't guarantee any kind of order.

  First build the list and save it to a variable (choose one way):

  // First, split into two by finding the opening parenthesis - .split()
  // Get the part that comes after it - [1]
  // Get rid of the second parenthesis - .slice()
  // Make an array from the names by splitting on commas - .split()
  var arguments = GetFormula.split('(')[1].slice(0, -1).split(',');
  
  // Also another way to do it with a regexp (Does the job, looks bad)
  // Splits on both parenthesis, gets what's in between of them
  // Then split on commas to make an array
  var arguments = GetFormula.split( /[\(\)]/ )[1].split(',');
  

  Finally, start constructing the final string:

  // GetFormula string, from after '#' and until '('  - included
  // e.g. 'MinimumLivingExpenses('
  var finalString = GetFormula.slice(1, GetFormula.indexOf('(') + 1);
  
  // For each argument, get its value from the object,
  // surround with quotes and add a comma
  arguments.forEach(function(argument){
      finalString += '"' + variables[argument] + '",';
  });
  
  // Replace the last comma with a closing parenthesis
  finalString = finalString.slice(0, -1) + ')';
  
  // Or another way to do it - with a regexp
  // finalString.replace(/,$/, ')')
  
  alert('Clarifying your question got you this string:' + finalString);
  

Update I don't know, what comes in the name in the first 12 chars, that you are only getting the next 999 chars, which is why I left your logic unchanged. But you could use name.slice(12) to get from 12th index to the end of the string.

Answer 2

If you really mean you want to do a substitution in a string, then you can use replace for that:

var LE_TotalAnnualIncome = "50000";
var LE_TypeOfSP = "Single";
var LE_NoDependants = "1";
var LE_Customer = "3000";
    
var str = "MinimumLivingExpenses(LE_TotalAnnualIncome,LE_TypeOfSP,LE_NoDependants,LE_Customer)";
str = str.replace("LE_TotalAnnualIncome", LE_TotalAnnualIncome)
         .replace("LE_TypeOfSP", LE_TypeOfSP)
         .replace("LE_NoDependants", LE_NoDependants)
         .replace("LE_Customer", LE_Customer);
console.log(str);

When called with a string as the first argument, it will replace the first occurrence of that string with the second argument.