可变范围和使用qUnit进行测试

Question

I'm new to qUnit testing and having trouble to understand why my variable "a" passes a scope test, even if the test is called before "a" was defined. When I log out "a" it behaves as expected. Can anyone give me a hint?

Here's the code:

function outer() {
    test('inside outer', function (assert) {
        assert.equal(typeof inner, "function", "inner is in scope"); //pass
        assert.equal(typeof a, "number", "a is in scope"); // pass
    });
    console.log(a); // undefined
    var a = 1;
    console.log(a); // 1
    function inner() {}

    var b = 2;

    if (a == 1) {
        var c = 3;
    }
}

outer();

Answer 1

Because of JavaScript's hoisting "a" is really declared at the top of your function but is initialized at the point in your code where you assign it a value.

So, when your code is interpreted, it actually looks more like this:

function outer() {
    var a, b, c;
    test('inside outer', function (assert) {
        assert.equal(typeof inner, "function", "inner is in scope"); //pass
        assert.equal(typeof a, "number", "a is in scope"); // pass
    });
    console.log(a); // undefined
    a = 1;
    console.log(a); // 1
    function inner() {}

    b = 2;

    if (a == 1) {
        c = 3;
    }
}

Also, take a look at JavaScript's function scoping rules: http://www.w3schools.com/js/js_scope.asp