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unpack array rest elements when given a right hand array expression

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This commit is contained in:
Sebastian McKenzie 2015-02-21 02:09:07 +11:00
parent 62556f6102
commit 299e462a29
3 changed files with 21 additions and 18 deletions
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18
lib/babel/transformation/transformers/es6/destructuring.js
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@ -163,13 +163,16 @@ var hasRest = function (pattern) {
};
DestructuringTransformer.prototype.canUnpackArrayPattern = function (pattern, arr) {
// not an array so there's no way we can deal with this
if (!t.isArrayExpression(arr)) return false;
if (pattern.elements.length < arr.elements.length) return false;
// pattern has less elements than the array and doesn't have a rest so some
// elements wont be evaluated
if (pattern.elements.length < arr.elements.length && !hasRest(pattern)) return false;
// deopt on holes
for (var i = 0; i < pattern.elements.length; i++) {
var elem = pattern.elements[i];
if (!elem) return false; // hole
if (t.isRestElement(elem)) return false;
if (!pattern.elements[i]) return false;
}
return true;
@ -177,7 +180,12 @@ DestructuringTransformer.prototype.canUnpackArrayPattern = function (pattern, ar
DestructuringTransformer.prototype.pushUnpackedArrayPattern = function (pattern, arr) {
for (var i = 0; i < pattern.elements.length; i++) {
this.push(pattern.elements[i], arr.elements[i]);
var elem = pattern.elements[i]
if (t.isRestElement(elem)) {
this.push(elem.argument, t.arrayExpression(arr.elements.slice(i)));
} else {
this.push(elem, arr.elements[i]);
}
}
};

4
test/fixtures/transformation/es6-destructuring/array-unpack-optimisation/actual.js vendored
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@ -1,9 +1,9 @@
// opt
var [a, b] = [1, 2];
var [[a, b]] = [[1, 2]];
var [a, b, ...c] = [1, 2, 3, 4];
var [[a, b, ...c]] = [[1, 2, 3, 4]];
// deopt
var [a, b] = [1, 2, 3];
var [[a, b]] = [[1, 2, 3]];
var [a, b, ...items] = [1, 2, 3];
var [[a, b, ...items]] = [[1, 2, 3]];

17
test/fixtures/transformation/es6-destructuring/array-unpack-optimisation/expected.js vendored
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@ -5,6 +5,12 @@ var a = 1;
var b = 2;
var a = 1;
var b = 2;
var a = 1;
var b = 2;
var c = [3, 4];
var a = 1;
var b = 2;
var c = [3, 4];
// deopt
var _ref = [1, 2, 3];
@ -13,14 +19,3 @@ var b = _ref[1];
var _ref2 = [1, 2, 3];
var a = _ref2[0];
var b = _ref2[1];
var _ref3 = [1, 2, 3];
var a = _ref3[0];
var b = _ref3[1];
var items = _ref3.slice(2);
var _ref4 = [1, 2, 3];
var a = _ref4[0];
var b = _ref4[1];
var items = _ref4.slice(2);