What is the correct way to check if a global variable exists?

Question

JSLint is not passing this as a valid code:

/* global someVar: false */
if (typeof someVar === \"undefined\") {
    var someVar = \"hi!\";
}

<

Answer 1

/**
 * @param {string} nameOfVariable
 */
function globalExists(nameOfVariable) {
    return nameOfVariable in window
}

It doesn't matter whether you created a global variable with var foo or window.foo — variables created with var in global context are written into window.