Snippet variable transform in some locations

Question

For example:

export const setVisibilityFilter = (filter) => ({
  type: 'SET_VISIBILITY_FILTER',
  filter
})

The name of the function setVisibilityFilter has camelCase. The same in the written version in uppercase characters separated by underscores: SET_VISIBILITY_FILTER

I want to make a snippet out of it. I want that after entering any text in the snippet variable, in the second place the uppercase characters separated by underscores were created from this text.

So that I do not have to write it for the second time, only in large letters ...

Is it possible in a snippet and how to do it?

Answer 1

vscode 1.25 did add transforms on snippet tabstops, so no need for a pre-selection. This version works, and with any number of camelCase words, like "camelCase", "camelCaseCaseCase", etc.

"test3": {
    "prefix": "seps",
    "body": [
        "export const $1 = (filter) => ({",
            "type: '${1/([a-z]*)(([A-Z])+([a-z]+))?/${1:/upcase}${2:+_}$3${4:/upcase}/g}',",
            "filter",
        "})"
    ],
    "description": "underscore separators"
}

See my similar answer convert from camelCase to all CAPS_WITH_SEPARATORS