ASCII Triangles

C, 58 bytes

i;f(n){for(i=2*n;~i--;printf(i<n?"-":"|%*c\n",2*n-i,92));}

--

Thanks to @Steadybox who's comments on this answer helped me shave a few bytes in my above solution

Javascript (ES6), 97 85 81 75 74 bytes

n=>(g=(n,s)=>n?g(--n,`|${" ".repeat(n)}\\
`+s):s)(n,"")+"-".repeat(n&&n+1)

Turns out I wasn't using nearly enough recursion

f=n=>(g=(n,s)=>n?g(--n,`|${" ".repeat(n)}\\
`+s):s)(n,"")+"-".repeat(n&&n+1)

console.log(f(0))
console.log(f(1))
console.log(f(2))
console.log(f(3))
console.log(f(4))

05AB1E, 16 15 16 bytes

Saved a byte thanks to Adnan

FðN×…|ÿ\}Dg'-×»?

Try it online!

Explanation

F       }         # for N in range [0 ... input-1]
 ðN×              # push <space> repeated N times
    …|ÿ\          # to the middle of the string "|\"
         Dg       # get length of last string pushed
           '-×    # repeat "-" that many times
              »   # join strings by newline
               ?  # print without newline