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     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

User · Answer

JavaScript actually does support encapsulation  through a method that involves hiding members in closures  Crockford   That said  it s sometimes cumbersome  and the underscore convention is a pretty good convention to use for things that are sort of private  but that you don t actually need to hide

User · Answer

Only conventions  Or is there more behind the underscore prefix     Apart from privacy conventions  I also wanted to help bring awareness that the underscore prefix is also used for arguments that are dependent on independent arguments  specifically in URI anchor maps  Dependent keys always point to a map   Example   from  https   github com mmikowski urianchor        uriAnchor setAnchor     page      profile      page          uname      wendy       online     today            The URI anchor on the browser search field is changed to      page profile uname wendy online today   This is a convention used to drive an application state based on hash changes

User · Answer

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

User · Answer

Welcome to 2019   It appears a proposal to extend class syntax to allow for   prefixed variable to be private was accepted  Chrome 74 ships with this support     prefixed variable names are considered private by convention but are still public      This syntax tries to be both terse and intuitive  although it s rather different from other programming languages        Why was the sigil   chosen  among all the Unicode code points            was the initial favorite  but it was taken by decorators  TC39 considered swapping decorators and private state sigils  but the committee decided to defer to the existing usage of transpiler users      would cause compatibility issues with existing JavaScript code  which has allowed   at the start of an identifier or  public  property name for a long time          This proposal reached Stage 3 in July 2017  Since that time  there has been extensive thought and lengthy discussion about various alternatives      In the end  this thought process and continued community engagement led to renewed consensus on the proposal in this repository  Based on that consensus  implementations are moving forward on this proposal    See https   caniuse com  feat mdn-javascript classes private class fields

User · Answer

import export is now doing the job with ES6  I still tend to prefix not exported functions with   if most of my functions are exported   If you export only a class  like in angular projects   it s not needed at all   export class MyOpenClass       open             doStuff            this  privateStuff            return close                privateStuff          only as a convention          function close          this is really private

User · Answer

JSDoc 3 allows you to annotate your functions with the  access private  previously the  private tag  which is also useful for broadcasting your intent to other developers - http   usejsdoc org tags-access html

[javascript] Underscore prefix for property and method names in JavaScript

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