How to remove the leading/trailing spaces within $…$ in JavaScript? [duplicate]

This doesn’t work and will give $1$ (expected: $1234$):

"$ 1234 $".replace(/$ *(.+?) *$/, "$$1$")

On the other hand,

"$ 1234 $".replace(/$ *(.+?) *$/, "$ $1$")

returns $ 1234$ correctly.