[Vuejs]-Using Vue JS $refs in function

Using the . notation you’re directly pointing to the name you’ve supplied after the . operator on a JS object.

To dynamically assign the accessing object key, you’ll need an approach like this:

this.$refs[fieldSwitchName].focus()

If switchToField is a variable, you need call $ref as array:

switchToField(fieldSwitchName, fieldValue, fieldLength) {
    if (String(this.fieldValue).length >= fieldLength) {
        this.$refs[fieldSwitchName].focus();
    }
}