Using the variable "name" doesn't work with a JS object

Question

The behaviour can be seen in this little snippet (execute it as a global script):

var name = {};
name.FirstName = 'Tom';
alert(name.FirstName);

The alert yields undefined in Chrome but works in IE and Firefox. I also get a weird value when I do

alert(name);

Answer 1

window.name has a special purpose, and is supposed to be a string. Chrome seems to explicitly cast it to a string, so var name = {}; actually ends up giving the global variable name (i.e. window.name) a value of "[object Object]". Since it's a primitive, properties (name.FirstName) won't "stick."

To get around this issue, don't use name as a global variable.

Answer 2

Your name variable is actually window.name, because top-level variables declared with var are attached to the global object.

The HTML5 spec requires that window.name is a DOMString. This means that the value of window.name can only be a sequence of characters, not an object.

In Chrome, an attempt to use window.name to store anything except a primitive string will coerce the value to a primitive string. For example:

window.name = {};
window.name === "[object Object]"; // true

You can avoid this problem by using a name variable that is not in the top-level scope:

(function() {
    var name = {};
    // this `name` is not `window.name`
    // because we're not in the top-level scope

    console.log(name);
})();

Answer 3

With ES6+, you could write your code as let name or const name. This won't assign it or try to override window.name. More on that here.

let name = {};
name.FirstName = 'Tom';
alert(name.FirstName);

Answer 4

window.name is used to set the name of the window, and since the window name can only be a string, anything you set to window.name is converted to a string. And strings, as primitive values, cannot have properties. The solution is to use a different variable name or a different scope.

Alternatively, you can use window.name as you like if you have this code first. I don't recommend this at all, but, just as a proof of concept:

(function () {
    var _name;
    window.__defineGetter__('name', function () {
        return _name;
    });
    window.__defineSetter__('name', function (v) {
        _name = v;
    });
})();

Additionally, you should use {} in place of new Object. Besides being more concise, it is also more efficient and more explicit.