typeGuardsInRightOperandOfOrOrOperator.ts(44,25): error TS2339: Property 'toString' does not exist on type 'never'.


==== typeGuardsInRightOperandOfOrOrOperator.ts (1 errors) ====
    // In the right operand of a || operation, 
    // the type of a variable or parameter is narrowed by any type guard in the left operand when false, 
    // provided the right operand contains no assignments to the variable or parameter.
    function foo(x: number | string) {
        return typeof x !== "string" || x.length === 10; // string
    }
    function foo2(x: number | string) {
        // modify x in right hand operand
        return typeof x !== "string" || ((x = 10) || x); // string | number
    }
    function foo3(x: number | string) {
        // modify x in right hand operand with string type itself
        return typeof x !== "string" || ((x = "hello") || x); // string | number
    }
    function foo4(x: number | string | boolean) {
        return typeof x === "string" // string | number | boolean
            || typeof x === "number"  // number | boolean
            || x;   // boolean
    }
    function foo5(x: number | string | boolean) {
        // usage of x or assignment to separate variable shouldn't cause narrowing of type to stop
        var b: number | boolean;
        return typeof x === "string" // string | number | boolean
            || ((b = x) || (typeof x === "number"  // number | boolean
            || x));   // boolean
    }
    function foo6(x: number | string | boolean) {
        // Mixing typeguard
        return typeof x === "string" // string | number | boolean
            || (typeof x !== "number" // number | boolean
            ? x // boolean
            : x === 10) // number 
    }
    function foo7(x: number | string | boolean) {
        var y: number| boolean | string;
        var z: number| boolean | string;
        // Mixing typeguard narrowing
        return typeof x === "string"
            || ((z = x) // number | boolean
            || (typeof x === "number"
            // change value of x
            ? ((x = 10) && x.toString()) // number | boolean | string
            // do not change value
            : ((y = x) && x.toString()))); // number | boolean | string
                            ~~~~~~~~
!!! error TS2339: Property 'toString' does not exist on type 'never'.
    }
    