Why variable name is set by default in browser?

Question

I need help understanding something that I'm learning. Some lines of my code set a variable, name, which holds a name for a user and is set when an element is clicked.

The problem I've discovered is even without clicking the element, a user may still access it in the console.

I thought something was wrong with my code but I found the same accessing it on another site; for instance, accessing the variable on facebook yields "_e_0MDe". Other sites yield empty strings, like "".

Why does this happen? Thank you.

"_I tried accessing variable name under facebook_" What **exactly** did you do? — takendarkk, Mar 17 '17 at 20:06
Your question is a little unclear. Could you provide code examples? — christopher, Mar 17 '17 at 20:06
In javascript, you don't have to define your variables with `var`. as soon as you assign a value, it will be defined. — serdar.sanri, Mar 17 '17 at 20:06
is `name` a global variable, or an attribute of a DOM element, or what exactly? — le_m, Mar 17 '17 at 20:06
https://developer.mozilla.org/en-US/docs/Web/API/Window/name — JJJ, Mar 17 '17 at 20:06
@guyfawkes If you don't use `var`, you're going to have a bad day… — deceze, Mar 17 '17 at 20:07
`name` is a reserved word. You should use more specific variable names in the future. — Goose, Mar 17 '17 at 20:07
http://stackoverflow.com/questions/6381425/is-there-a-spec-that-the-id-of-elements-should-be-made-global-variable — epascarello, Mar 17 '17 at 20:08
Why are you responding to the posted answers, but not to any of the questions we asked you? — takendarkk, Mar 17 '17 at 20:09
@deceze If you don't use `const`/`let`, you're going to have a bad day... — Sterling Archer, Mar 17 '17 at 20:09

Daniel A. White · Accepted Answer · 2017-03-17T20:09:43.487

4

window.name is just part of the DOM API. Facebook must be setting it.

If you declare a variable in a bare script tag, its treated as part of window

<script>
  var name = 'foo';
  console.log(window.name); // "foo"
</script>

In order to prevent that use a function to create a new scope (or use let)

<script>
  (function() {
    var name = 'foo';
  })();
  console.log(window.name); // what ever it was before this function call
</script>

edited Mar 17 '17 at 20:09

answered Mar 17 '17 at 20:06

Daniel A. White

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oh okay... please do you have a list of such? – james Oduro Mar 17 '17 at 20:08
Seems like the most plausible explanation, given that OP probably uses a global variable. – le_m Mar 17 '17 at 20:08
@jamesOduro a list of what? – Daniel A. White Mar 17 '17 at 20:08
1

@jamesOduro Type "window" in the console and see what properties it has. – JJJ Mar 17 '17 at 20:09
Thank you so much...that was much understandable – james Oduro Mar 17 '17 at 20:21

score 0 · Answer 2 · edited Mar 17 '17 at 21:57

JavaScript, like many scripting languages, can be very loose in variable declarations and initializations. This allows for quick development, but also means you have to be aware of scoping.

What you may be seeing is a collision in the global scope. By default, browsers have a global object called, window. This object can be used anywhere, in any function that you declare.

When you don't initialize a variable in a block with one of the reserved words (var, let, function, class, import, const), the global scope may be used. For instance, the following are equivalent:

```
name = 'foo';
window.name = 'foo';
```

To help avoid syntax mistakes, developers often include a magical phrase at the top of their code:

```
"use strict";
```

More information can be found on John Resig's strict mode site.

Why variable name is set by default in browser?

2 Answers2