diffProperties() — react Function Reference

Source Code

packages/react-native-renderer/src/ReactNativeAttributePayload.js lines 269–443

function diffProperties(
  updatePayload: null | Object,
  prevProps: Object,
  nextProps: Object,
  validAttributes: AttributeConfiguration,
): null | Object {
  let attributeConfig;
  let nextProp;
  let prevProp;

  for (const propKey in nextProps) {
    attributeConfig = validAttributes[propKey];
    if (!attributeConfig) {
      continue; // not a valid native prop
    }

    prevProp = prevProps[propKey];
    nextProp = nextProps[propKey];

    // functions are converted to booleans as markers that the associated
    // events should be sent from native.
    if (typeof nextProp === 'function') {
      nextProp = (true: any);
      // If nextProp is not a function, then don't bother changing prevProp
      // since nextProp will win and go into the updatePayload regardless.
      if (typeof prevProp === 'function') {
        prevProp = (true: any);
      }
    }

    // An explicit value of undefined is treated as a null because it overrides
    // any other preceding value.
    if (typeof nextProp === 'undefined') {
      nextProp = (null: any);
      if (typeof prevProp === 'undefined') {
        prevProp = (null: any);
      }
    }

    if (removedKeys) {
      removedKeys[propKey] = false;
    }

    if (updatePayload && updatePayload[propKey] !== undefined) {
      // Something else already triggered an update to this key because another
      // value diffed. Since we're now later in the nested arrays our value is
      // more important so we need to calculate it and override the existing
      // value. It doesn't matter if nothing changed, we'll set it anyway.

      // Pattern match on: attributeConfig
      if (typeof attributeConfig !== 'object') {
        // case: !Object is the default case
        updatePayload[propKey] = nextProp;
      } else if (
        typeof attributeConfig.diff === 'function' ||
        typeof attributeConfig.process === 'function'
      ) {
        // case: CustomAttributeConfiguration
        const nextValue =
          typeof attributeConfig.process === 'function'
            ? attributeConfig.process(nextProp)
            : nextProp;
        updatePayload[propKey] = nextValue;
      }
      continue;
    }

    if (prevProp === nextProp) {
      continue; // nothing changed
    }

    // Pattern match on: attributeConfig
    if (typeof attributeConfig !== 'object') {
      // case: !Object is the default case
      if (defaultDiffer(prevProp, nextProp)) {
        // a normal leaf has changed
        (updatePayload || (updatePayload = ({}: {[string]: $FlowFixMe})))[
          propKey
        ] = nextProp;
      }
    } else if (