JS Intellisense not detecting ES6 Symbol properties assigned after Initialization

• VS Code Version: 1.54.3
• OS Version: Windows 10 Pro, version 20H2, build 19042.804

Steps to Reproduce:

1. Initialize a Symbol
2. Initialize an empty object literal
3. Assign the object a function, using the symbol as its property

The following code also demonstrates some of the steps to reproduce:

const symKey = Symbol();


/** @namespace */
var objLiteral = {
    literalPublicFn1() {},

    /**
     * You found the secret fn!
     */
    [symKey]() {},
};


/** @namespace */
var objAssigned = {};

/** @memberof objAssigned */
objAssigned.laterPublicFn1 = function() {};

/** 
 * You found the secret fn!
 * @memberof objAssigned 
 * */
objAssigned[symKey] = function () {}

For both objects, the string properties are picked up by Intellisense and autocompleted as expected. However, Intellisense only provides function info for the symbol on the objLiteral object, where the symbol property was declared as part of the literal. For the objAssigned object, where the symbol property was assigned after initialization, no function info is provided.

In other words, intellisense works when calling objLiteral[symKey]() but not when calling objAssigned[symKey]()

Does this issue occur when all extensions are disabled?: Yes

Start with the JavaScript reproduction in the issue and investigate the TypeScript language-service handling of computed Symbol properties assigned after object initialization. Compare IntelliSense for objLiteralsymKey with objAssignedsymKey, and consider the issue complete when both provide the function information shown for the literal case.