There are several ways to fix Vue.js watcher memory leak issues. Here are some techniques that can help improve the performance of your application:

1. Use Deep Watchers: Instead of using a simple watch, use deep watchers if you want to track changes in nested properties. This will make sure that all changes will be detected and trigger a re-render.

Example:

watch: {
  '$data': 'yourFunction',
  deep: true
}

2. Limit Watchers: If you have numerous watchers in your application, try to limit the number of watchers and make sure that they are only necessary. This will help reduce memory usage.

3. Use Computed Properties Instead of Watchers: If possible, use computed properties instead of watchers because they are memoized and cached, which can improve performance by preventing unnecessary re-computation.

Example:

computed: {
  yourFunction: function() {
    // Your code here
  }
}

4. Use Lodash debounce or throttle functions: If you have watchers that fire frequently, use lodash's debounce or throttle function to limit the number of times your watcher is called per second. This will prevent unnecessary re-renders and improve performance.

Example:

import {debounce} from 'lodash';

export default {
  data() {
    return {
      yourData: ''
    };
  },
  watch: {
    '$data': debounce(function() {
      // Your code here
    }, 500)
  }
}

5. Use Vuex for State Management: If your application becomes large, use Vuex for state management to manage the application's state. It helps in reducing memory usage by managing state globally and avoiding unnecessary re-renders.

Example:

import Vue from 'vue';
import Vuex from 'vuex';

Vue.use(Vuex);

export default new Vuex.Store({
  state: {
    yourData: ''
  },
  mutations: {
    setYourData(state, data) {
      state.yourData = data;
    }
  },
  actions: {
    updateYourData({commit}, data) {
      commit('setYourData', data);
    }
  }
});

By implementing these techniques, you can effectively address memory leak issues in Vue.js applications and improve the performance of your application.