Playground Proposal: Mallet operator#516
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sebmck merged 2 commits intobabel:masterfrom Jan 17, 2015
jridgewell:mallot
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Playground Proposal: Mallet operator#516sebmck merged 2 commits intobabel:masterfrom jridgewell:mallot
sebmck merged 2 commits intobabel:masterfrom
jridgewell:mallot
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The mallet operator is similar to the current memoization operator, except it can be used outside of just objects. In Ruby, it’s almost the same as `a = a || b`. Note that only `nil` and `false` are falsey in Ruby. I’ve defined it as `== null`, though that could be changed to any JS falsey value.
sebmck
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Playground Proposal: Mallet operator
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Thanks! I'll have to refactor this a bit as there's a lot of duplicate code shared between this and the memoization operator. |
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@jridgewell Can you also send a pull request that adds this to the docs? Thanks! |
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This will break because obj is going to be evaluated multiple times.
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This is to avoid an unnecessary var declaration.
// obj.x ||= 2
if (!obj.x) obj.x = 2
// As opposed to
var _obj = obj;
if (!_obj.x) _obj.x = 2
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What about setters defined on global? We can't evaluate nodes more than what's expected. It's the same reason that we have to work out the computed key etc.
Object.defineProperty(global, "obj", {
get: function () {
// this is going to get called every time you reference `obj` when it should only be evaluated a limited amount of times
}
});
obj ||= 2; // should only "get" obj once
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😞 Damn, hadn't considered that.
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Released as of 2.13.0. |
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loganfsmyth
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The mallet will check to see if the variable is falsey, and if it is, override it. It's almost the same as `a = a || b`. Re: babel/babel#516
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https://github.com/jridgewell/proposal-logical-assignment I'm bringing it [back](babel#516). 😉
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* Proposal: Logical Assignment Operators https://github.com/jridgewell/proposal-logical-assignment I'm bringing it [back](#516). 😉 * Use expectPlugin * Add to stage 0 preset * Add logicalAssignment missing plugin log stuff
aminmarashi
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* Proposal: Logical Assignment Operators https://github.com/jridgewell/proposal-logical-assignment I'm bringing it [back](babel#516). 😉 * Use expectPlugin * Add to stage 0 preset * Add logicalAssignment missing plugin log stuff
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The mallet operator is similar to the current memoization operator,
except it can be used outside of just objects.
In Ruby, it’s almost the same as
a = a || b. Note that onlynilandfalseare falsey in Ruby. I’ve defined it as== null, though thatcould be changed to any JS falsey value.