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perf(mangler): improve mangleScope perf #854

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merged 1 commit into from May 16, 2018
Merged

perf(mangler): improve mangleScope perf #854

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30 changes: 17 additions & 13 deletions packages/babel-plugin-minify-mangle-names/src/index.js
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Expand Up @@ -320,18 +320,13 @@ module.exports = babel => {
}
mangler.visitedScopes.add(scope);

// Helpers to generate names
let i = 0;
function getNext() {
return mangler.charset.getIdentifier(i++);
}
function resetNext() {
i = 0;
}

const bindings = scopeTracker.bindings.get(scope);
const names = [...bindings.keys()];

// A counter to generate names and reset
// so we can reuse removed names
let counter = 0;

/**
* 1. Iterate through the list of BindingIdentifiers
* 2. Rename each of them in-place
Expand All @@ -341,18 +336,27 @@ module.exports = babel => {
* because (2) we rename in place and update the bindings
* as we traverse through the keys
*/
for (let i = 0; i < names.length; i++) {
const oldName = names[i];
for (const oldName of names) {
const binding = bindings.get(oldName);

if (mangler.canMangle(oldName, binding, scope)) {
let next;
do {
next = getNext();
next = mangler.charset.getIdentifier(counter++);
} while (!mangler.isValidName(next, binding, scope));

// Reset so variables which are removed can be reused
resetNext();
//
// the following is an assumtion (for perf)
// the length 3 is an assumption that if the oldName isn't
// 1 or 2 characters, then probably we are not going to find
// a name - because for almost all usecases we have 1 or 2
// character new names only. And for the edge cases where
// one scope has lots and lots of variables, it's okay to
// name something with 3 characters instead of 1
if (oldName.length < 3) {
counter = 0;
}

// Once we detected a valid `next` Identifier which could be used,
// call the renamer
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