Attaching Javascript documentation to VSCode

Hi, I’m using Visual Studio Code 1.61.2 to write javascript.
Let’s say i write something like this

function longest(list) {
  const lengths =, index) => ({
    length: str.length


  const i = lengths.reduce(
    (acc, obj) => (obj.length > acc ? obj.index : acc),

  return list[i];

Using a Mac I can put the cursor over either console or dir and press Command and view the documentation in a popup.

This does not work on the .map method.
How do I configure VSCode so that I can see the method information for .map ?

I want it to link to an explanation as comprehensive as



Hi @jonbangbanggreenwood, the language service doesn’t know that your list parameter is supposed to be an array; it can infer the type to some extent if you add a default value (say), but to be explicit you can add JSDoc annotations:

 * @param {string[]} list 
 * @returns {string}
function longest (list) {
  // ...
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