Underscore prefix for property and method names in JavaScript

Question

Is the underscore prefix in JavaScript only a convention, like for example in Python private class methods are?

From the 2.7 Python documentation:

“Private” instance variables that cannot be accessed except from inside an object don’t exist in Python. However, there is a convention that is followed by most Python code: a name prefixed with an underscore (e.g. _spam) should be treated as a non-public part of the API (whether it is a function, a method or a data member).

Does this also apply to JavaScript?

Take for example this JavaScript code:

function AltTabPopup() {
    this._init();
}

AltTabPopup.prototype = {
    _init : function() {
        ...
    }
}

Also, underscore prefixed variables are used.

    ...
    this._currentApp = 0;
    this._currentWindow = -1;
    this._thumbnailTimeoutId = 0;
    this._motionTimeoutId = 0;
    ...

Only conventions? Or is there more behind the underscore prefix?

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I admit my question is quite similar to this question, but it didn't make one smarter about the significance of the underscore prefix in JavaScript.

Answer 1

That's only a convention. The Javascript language does not give any special meaning to identifiers starting with underscore characters.

That said, it's quite a useful convention for a language that doesn't support encapsulation out of the box. Although there is no way to prevent someone from abusing your classes' implementations, at least it does clarify your intent, and documents such behavior as being wrong in the first place.