javascript variable shows as NaN when passed to a function

Question

a=["s21aSi"]

gPf = function(a) {
    var c;
    a.forEach(function(b) {
        c = b
    })

    gPg(c);
    console.log('Inside gPf '+c)
}

gPg = function(z) {
    console.log('Inside gPg', +z)
}

gPf(a)

Why does z show as Nan when I do console.log inside gPg . It's a string inside gPf but show Nan when it's inside gPg

Answer 1

delete '+' before z:

gPg = function(z) {
    console.log('Inside gPg', z)
}

or

gPg = function(z) {
    console.log(`Inside gPg ${z}`)
}

Answer 2

Because you are changing the signal of a Not-A-Number , when you add before a number a signal(+ or -) you a force change the signal of this number, when you add a signal before a string, the JS force a convertion in this string to number, but the string isn't a number, so JS convert this to NaN , see here to more details.

So to your code to work, you need remove + before a variable z , like this:

 a = ["s21aSi"] gPf = function(a) { var c; a.forEach(function(b) { c = b }) gPg(c); console.log('Inside gPf:', c) } gPg = function(z) { console.log('Inside gPg:', z) } gPf(a)

Answer 3

'Inside gPf '+c the plus sign (+) is being used to concatenate 2 strings.

'Inside gPg', +z the plus sign (+) is used as a math (addition) function