Javascript ReferenceError: Invalid left-hand side in assignment

So lately was trying some silly syntax with javascript, logically it seems to work, but throw away your dry logic!

Most of us who have been pawing at some raw JS knows  undefined || "hi" would result in "hi", on the same lines, /me tried :

> obj={}
> obj["prop"] || obj["prop"] = "newprop"
    ReferenceError: Invalid left-hand side in assignment
    arguments: Array[0]
    get message: function () { [native code] }
    get stack: function () { [native code] }
    set message: function () { [native code] }
    set stack: function () { [native code] }
    type: "invalid_lhs_in_assignment"
    <strong>proto</strong>: Error
> obj["prop"] = obj["prop"] || "newprop"
> obj.prop
 # Works this way ^_ ^

One of my friend @Altreus said "Lack of ||= saddens me" and @jasonmulligan solution helped!


  • ||= is much needed.
  • obj['prop'] ||= "fun"
  • There is already a proposal in ES5 for this now!

Happy hacking, hope we shall have more fun with more JS :)

EDIT 0 suggested by charliesome:

obj["prop"] || (obj["prop"] = "newprop");

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