How to overlay two areas under the curve in a plot?

i've got a function setup to plot the area under a curve of a gaussian distribution and i'd like to be able to highlight two areas on the same plot. In this case it should be mirrored.

areaplotter <- function(x1,x2){
  x <- seq(from=-4,to=4,len=100)
  plot(x,dnorm(x),type='l')
  jj <- seq(from=x1,to=x2,len=100)
  polygon(x=c(jj,x2,x1),y=c(dnorm(jj),0,0),col='red')
}

Essentially i'd like to get the two following plots in one

areaplotter(-4,qnorm(0.05))
areaplotter(qnorm(1-0.05),4)

Right now i managed to put them next to each other with par(mfrow = c(1,2)) but i want the shaded areas to appear on one plot

Is there a simple syntax or is there another funtion i should use? thanks in advance.

I tried using the lines() function but I'm new to R and it didnt work so i might done it wrong

Solution

I simplified the function so that it only needs the alpha level.

areaplotter <- function(alpha = 0.05){
  x <- seq(from = -4, to = 4, len = 100)
  plot(x, dnorm(x), type = 'l')
  
  x1 <- qnorm(alpha)
  x2 <- qnorm(1 - alpha)
  jj1 <- seq(from = x[1], to = x1, len = 100)
  jj2 <- seq(from = x2, to = x[100], len = 100)
  polygon(x = c(jj1, x1, x[1]), y = c(dnorm(jj1), 0, 0), col = 'red')
  polygon(x = c(jj2, x[100], x2), y = c(dnorm(jj2), 0, 0), col = 'red')
}

areaplotter()

areaplotter(0.1)