Function producerRecomputeValue

packages/core/primitives/signals/src/computed.ts:132–172

(node: ComputedNode<unknown>)

    },

    producerRecomputeValue(node: ComputedNode<unknown>): void {
      if (node.value === COMPUTING) {
        // Our computation somehow led to a cyclic read of itself.
        throw new Error(
          typeof ngDevMode !== 'undefined' && ngDevMode ? 'Detected cycle in computations.' : '',
        );
      }

      const oldValue = node.value;
      node.value = COMPUTING;

      const prevConsumer = consumerBeforeComputation(node);
      let newValue: unknown;
      let wasEqual = false;
      try {
        newValue = node.computation();
        // We want to mark this node as errored if calling `equal` throws; however, we don't want
        // to track any reactive reads inside `equal`.
        setActiveConsumer(null);
        wasEqual =
          oldValue !== UNSET &&
          oldValue !== ERRORED &&
          newValue !== ERRORED &&
          node.equal(oldValue, newValue);
      } catch (err) {
        newValue = ERRORED;
        node.error = err;
      } finally {
        consumerAfterComputation(node, prevConsumer);
      }

      if (wasEqual) {
        // No change to `valueVersion` - old and new values are
        // semantically equivalent.
        node.value = oldValue;
        return;
      }

      node.value = newValue;
      node.version++;
    },
  };
})();