Array.filter callback parameter should not be required to return a boolean

[mjohnsonengr]

The TypeScript definition for Array.filter specifies the callback must return a boolean, thus the code example at the bottom of this post fails to compile. Here's the current definition:

filter(callbackfn: (value: T, index: number, array: T[]) => boolean, thisArg?: any): T[];

The spec says this about the callback parameter:

callbackfn should be a function that accepts three arguments and returns a value that is coercible to the Boolean value true or false.

Thus I propose the definition should be changed to:

filter(callbackfn: (value: T, index: number, array: T[]) => any, thisArg?: any): T[];

Note: using a double not-operator is a sufficient workaround with negligible implications

TypeScript Version:
1.8.7

Code
Playground

// the purpose is to weed out falsey values
let a = [1, 2, 3, undefined, 0, 42, ""].filter(i => i)
// "i => i" is an error because it does not return boolean
// the following has no error
let b = [1, 2, 3, undefined, 0, 42, ""].filter(i => !!i)

Expected behavior:
No compile errors

Actual behavior:
Compile errors

[RyanCavanaugh]

This appears to be a duplicate of issue #5850

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