This extension will list all symbols in a code file as plain text using vscode's built-in symbol processing capabilites.
Simply run ctrl + shift + p
-> List Symbols
and you will get output like the following in a new tab (Based on this example code):
class Calculator
constructor constructor
method appendNumber
method chooseOperation
method clear
method compute
variable computation
variable current
variable prev
method delete
method getDisplayNumber
variable decimalDigits
variable integerDigits
variable integerDisplay
property maximumFractionDigits
variable stringNumber
method updateDisplay