JavaScript 'strict mode' not working as expected?

Question

var test = function() {

    'use strict';

    var mapNames = {
        'name': 'City Name:',
        'coord.lat': 'Latitute:'
    };  

    for (var key in mapNames) {

        var names;

        if (mapNames[key]) {
            name = mapNames[key];
        } else {
            name = key;
        }
    }

    console.log(name);

}

test();

In the code above I made a mistake by declaring variable names and using name instead. I thought 'strict' mode would catch it but it didn't. Shouldn't this throw an error in this case?

Answer 1

A name global variable already exists, unrelated to your code; it represents the name of the current window, so you are assigning to an already existing variable.

window.name; // the name of the current window for cross-window communication

Everything on window is declared as a global - so it is not reference-erroring since it is assigning to a variable in an outer scope.

Super confusing :D

• window.name on MDN.
• HTML Specification, window name property .

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"use strict" would prevent defining new global variables, here we are performing an assignment to an existing variable, think of it as name is in the global scope, like window.Blob , window.console and so on.