Method set

packages/reactivity/src/baseHandlers.ts:142–192

(
    target: Record<string | symbol, unknown>,
    key: string | symbol,
    value: unknown,
    receiver: object,
  )

  }

  set(
    target: Record<string | symbol, unknown>,
    key: string | symbol,
    value: unknown,
    receiver: object,
  ): boolean {
    let oldValue = target[key]
    const isArrayWithIntegerKey = isArray(target) && isIntegerKey(key)
    if (!this._isShallow) {
      const isOldValueReadonly = isReadonly(oldValue)
      if (!isShallow(value) && !isReadonly(value)) {
        oldValue = toRaw(oldValue)
        value = toRaw(value)
      }
      if (!isArrayWithIntegerKey && isRef(oldValue) && !isRef(value)) {
        if (isOldValueReadonly) {
          if (__DEV__) {
            warn(
              `Set operation on key "${String(key)}" failed: target is readonly.`,
              target[key],
            )
          }
          return true
        } else {
          oldValue.value = value
          return true
        }
      }
    } else {
      // in shallow mode, objects are set as-is regardless of reactive or not
    }

    const hadKey = isArrayWithIntegerKey
      ? Number(key) < target.length
      : hasOwn(target, key)
    const result = Reflect.set(
      target,
      key,
      value,
      isRef(target) ? target : receiver,
    )
    // don't trigger if target is something up in the prototype chain of original
    if (target === toRaw(receiver) && result) {
      if (!hadKey) {
        trigger(target, TriggerOpTypes.ADD, key, value)
      } else if (hasChanged(value, oldValue)) {
        trigger(target, TriggerOpTypes.SET, key, value, oldValue)
      }
    }
    return result
  }

  deleteProperty(
    target: Record<string | symbol, unknown>,