Type guard does not work when its value is set to a variable.

[alexandretperez]

TypeScript Version: 2.7.0-dev.20171111

Code

// -- Errors here:
test(value: number | undefined) : number {
    let isNumber = typeof value == "number";
    if (isNumber && value > 0) // < -- TS2532: Object is possibly 'undefined'.
        return value * 10;

    return 0;
}

// -- No errors here:
test(value: number | undefined) : number{
    if (typeof value == "number" && value > 0)
        return value * 10;

    return 0;
}

Expected behavior:
No errors

Actual behavior:

TS2532: Object is possibly 'undefined'.

[ahejlsberg]

Duplicate of #12184.

[typescript-bot]

Automatically closing this issue for housekeeping purposes. The issue labels indicate that it is unactionable at the moment or has already been addressed.