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#JavaScript (ES6), 33 28 bytes

n=>eval(1+("*"+n).repeat(n))

Add 7 bytes if we need to allow for negative integers.

n=>eval(1+("*"+n).repeat(n<0?-n:n))

And add 4 bytes if 0 should be output for input 0

n=>n?eval(1+("*"+n).repeat(n<0?-n:n)):n

##Try It

f=
n=>eval(1+("*"+n).repeat(n))
o.innerText=f(i.value=3)
i.oninput=_=>o.innerText=f(+i.value)

<input id=i type=number><pre id=o>

##33 byte solution n=>eval(Array(n).fill(n).join*)