Select's activeItem prop does not work if items are not 'strings'

[jonavila]

Environment

• Package version(s): 3.6.1
• Browser and OS versions: Chrome 69

Steps to reproduce

1. Use the Select component '@blueprintjs/select' and use an array of objects for the items prop.
2. Specify the activeItem prop as one of the objects in the items prop
3. Provide a value prop.

Actual behavior

The activeItem is not highlighted when the select's popover opens showing the list of items

Expected behavior

activeItem should be highlighter

Possible solution

The activeItem prop works as expected when the list of items are of type 'string'. I believe this part of the source code is what's setting the itemRenderer modifiers:

https://github.com/palantir/blueprint/blob/develop/packages/select/src/components/query-list/queryList.tsx#L211

My guess is the equality of activeItem === item is failing for objects

[giladgray]

@jonavila the === check will definitely fail if the two objects are not exactly the same object. not objects that look the same but actually the same. this is a known limitation of the API. to fix it we'll have to introduce an itemComparator prop a la itemDisabled to allow customizing the equality check. see #1340.

example:

// actually the same instance
const obj = { prop: "yes" };
const obj2 = obj;
obj === obj2 // true

// look the same, separate instances
const a = { a: 5 };
const b = { a: 5 };
a === b // false