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[performance] Replace hasOwnProperty in child processing with typeof undefined check #3665

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merged 2 commits into from
Apr 22, 2015
Merged

[performance] Replace hasOwnProperty in child processing with typeof undefined check #3665

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5a431a1
Replace hasOwnProperty in child processing with typeof undefined check
Apr 13, 2015
ed70d35
Update code style
Apr 14, 2015
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2 changes: 1 addition & 1 deletion src/utils/ReactChildren.js
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Original file line number Diff line number Diff line change
Expand Up @@ -81,7 +81,7 @@ function mapSingleChildIntoContext(traverseContext, child, name, i) {
var mapBookKeeping = traverseContext;
var mapResult = mapBookKeeping.mapResult;

var keyUnique = !mapResult.hasOwnProperty(name);
var keyUnique = ('undefined' === typeof mapResult[name]);
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Normally we'd just write (mapResult[name] === undefined) – I assume that's no slower?

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typeof is about 20-25% faster than direct equality according to http://jsperf.com/hasownproperty-vs-in-vs-undefined/81

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We have a transpiler that can turn === undefined into === void 0 which is faster yet but ugly.

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We use the constant (string literal) on the right hand side. Which is triggering a lint warning which is failing the unit tests.

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I'll update to match the styling rules.

if (__DEV__) {
warning(
keyUnique,
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2 changes: 1 addition & 1 deletion src/utils/flattenChildren.js
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Expand Up @@ -22,7 +22,7 @@ var warning = require('warning');
function flattenSingleChildIntoContext(traverseContext, child, name) {
// We found a component instance.
var result = traverseContext;
var keyUnique = !result.hasOwnProperty(name);
var keyUnique = ('undefined' === typeof result[name]);
if (__DEV__) {
warning(
keyUnique,
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