next
Version:
The React Framework
90 lines (88 loc) • 4.04 kB
JavaScript
;
Object.defineProperty(exports, "__esModule", {
value: true
});
Object.defineProperty(exports, "useRouterBFCache", {
enumerable: true,
get: function() {
return useRouterBFCache;
}
});
const _react = require("react");
// When the flag is disabled, only track the currently active tree
const MAX_BF_CACHE_ENTRIES = process.env.__NEXT_ROUTER_BF_CACHE ? 3 : 1;
function useRouterBFCache(activeTree, activeStateKey) {
// The currently active entry. The entries form a linked list, sorted in
// order of most recently active. This allows us to reuse parts of the list
// without cloning, unless there's a reordering or removal.
// TODO: Once we start tracking back/forward history at each route level,
// we should use the history order instead. In other words, when traversing
// to an existing entry as a result of a popstate event, we should maintain
// the existing order instead of moving it to the front of the list. I think
// an initial implementation of this could be to pass an incrementing id
// to history.pushState/replaceState, then use that here for ordering.
const [prevActiveEntry, setPrevActiveEntry] = (0, _react.useState)(()=>{
const initialEntry = {
tree: activeTree,
stateKey: activeStateKey,
next: null
};
return initialEntry;
});
if (prevActiveEntry.tree === activeTree) {
// Fast path. The active tree hasn't changed, so we can reuse the
// existing state.
return prevActiveEntry;
}
// The route tree changed. Note that this doesn't mean that the tree changed
// *at this level* — the change may be due to a child route. Either way, we
// need to either add or update the router tree in the bfcache.
//
// The rest of the code looks more complicated than it actually is because we
// can't mutate the state in place; we have to copy-on-write.
// Create a new entry for the active cache key. This is the head of the new
// linked list.
const newActiveEntry = {
tree: activeTree,
stateKey: activeStateKey,
next: null
};
// We need to append the old list onto the new list. If the head of the new
// list was already present in the cache, then we'll need to clone everything
// that came before it. Then we can reuse the rest.
let n = 1;
let oldEntry = prevActiveEntry;
let clonedEntry = newActiveEntry;
while(oldEntry !== null && n < MAX_BF_CACHE_ENTRIES){
if (oldEntry.stateKey === activeStateKey) {
// Fast path. This entry in the old list that corresponds to the key that
// is now active. We've already placed a clone of this entry at the front
// of the new list. We can reuse the rest of the old list without cloning.
// NOTE: We don't need to worry about eviction in this case because we
// haven't increased the size of the cache, and we assume the max size
// is constant across renders. If we were to change it to a dynamic limit,
// then the implementation would need to account for that.
clonedEntry.next = oldEntry.next;
break;
} else {
// Clone the entry and append it to the list.
n++;
const entry = {
tree: oldEntry.tree,
stateKey: oldEntry.stateKey,
next: null
};
clonedEntry.next = entry;
clonedEntry = entry;
}
oldEntry = oldEntry.next;
}
setPrevActiveEntry(newActiveEntry);
return newActiveEntry;
}
if ((typeof exports.default === 'function' || (typeof exports.default === 'object' && exports.default !== null)) && typeof exports.default.__esModule === 'undefined') {
Object.defineProperty(exports.default, '__esModule', { value: true });
Object.assign(exports.default, exports);
module.exports = exports.default;
}
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