Assign value to a variable in node.js

Question

I'm a beginner with node.js and I have a problem after evaluating evalMath() function. Especially, assigning the value of Math2 to yScale.

Math2 is an input box of a web page, which is introduced a simple equation like 'Ir = Vr/R'. This string value is passed from the web page to the web server implemented on node.js. In there, the function evalMath() is executed, which replaces Vr (with a string) and R with a respective integer value. After executing this function is obtained something like this 'ANI0[i]-ANI5[i]/10', which is stored in the variable Math2. The function works perfectly. However, when Math2 is assign to yScale only saves 'Ir = Vr/R' and not the string obtained after executing the evalMath() --> 'ANI0[i]-ANI5[i]/10'. I don't know exactly why.

 if (yScale == 'Math2') {
    console.log('Math2 selected');
    evalMath(textAD0,textAD1,textAD2,textAD3,textAD4,Math2,Rb,Rc,R,yScale);
    yScale = Math2;
    console.log ("yScale: "+ yScale);
} else {
    console.log("Nothing to change :) - No eqn");
}

function evalMath(labelAD0, labelAD1, labelAD2, labelAD3,
                labelAD4, entry, entry1, entry2, entry3, entry4) {
    iAD0="",iAD1="",iAD2="",iAD3="",iAD4="",iR="",iRb="", iRc="", iEq="";

    var iAD0 = entry.search(labelAD0);
    var iAD1 = entry.search(labelAD1);
    var iAD2 = entry.search(labelAD2);
    var iAD3 = entry.search(labelAD3);
    var iAD4 = entry.search(labelAD4);
    var iR = entry.search('R');
    var iRb = entry.search('Rb');
    var iRc = entry.search('Rc');
    var iEq = entry.search('=');    

    if (iAD0 > "0"){ entry = entry.replace(labelAD0,'(ANI0[i]-ANI5[i])'); }
    else{console.log("Nothing to change AD0")}
    if (iAD1 > "0"){ entry = entry.replace(labelAD1,'(ANI1[i]-ANI5[i])'); }
    else{console.log("Nothing to change AD1")}
    if (iAD2 > "0"){ entry = entry.replace(labelAD2,'(ANI2[i]-ANI5[i])'); }
    else{console.log("Nothing to change AD2")}
    if (iAD3 > "0"){ entry = entry.replace(labelAD3,'(ANI3[i]-ANI5[i])'); }
    else{console.log("Nothing to change AD3")}
    if (iAD4 > "0"){ entry = entry.replace(labelAD4,'(ANI4[i]-ANI5[i])'); }
    else{console.log("Nothing to change AD4")}
    if (iRb > "0"){ entry = entry.replace('Rb',entry1); }
    else{console.log("Nothing to change Rb")}
    if (iRc > "0"){ entry = entry.replace('Rc',entry2); }
    else{console.log("Nothing to change Rc")}
    if (iR > "0"){ entry = entry.replace('R',entry3); }
    else{console.log("Nothing to change R")}
    if (iEq > "0"){ entry = entry.slice(iEq+1,entry.length); }
    else{console.log("Nothing to change iEq")}

    console.log("entry: " + entry);
    return entry;
}

Daphoque · Accepted Answer · 2017-08-07 11:37:09Z

When you pass a parameters to a function, just the value is passed and not the reference of the variable (for string, int, float, etc...). If you want to be able to modify the value of the parameters, pass it through an object :

var a = "hello";
var b = "moto"; 

var obj = {a: "hello", b: "moto"};

function c(p1, p2){ p1 = "yala"; p2="yele";}

c(a, b); // a == hello, b == moto, values not changed

function c2(p1) { p1.a = "yala"; p1.b = "yele";}

c2(obj); // obj.a == "yala", obj.b == "yele"

So in your case do the following :

var entries = {
 Math2: Math2,
 Rb: Rb,
 Rc: Rc,
 R:  R
 yScale: yScale
};


evalMath(textAD0,textAD1,textAD2,textAD3,textAD4,entries);
entries.yScale = entries.Math2;
console.log ("yScale: "+ entries.yScale);

Then replace prototype of evalMath with

   function evalMath(labelAD0, labelAD1, labelAD2, labelAD3,
            labelAD4, entries) {

En then in evalMath, replace all occurence of entry1 with entries.Math2, all occurence of entry2 with entries.Rb, all occurence of entry3 with entries.Rc, all occurence of entry4 with entries.R and all occurence off entry5 with entries.yScale

Warning if you affect some values to entries.SOMETHING it will be modified out of the function

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