MDN文档对该方法的描述如下

即形如Object.assign(obj1, obj2)的语法中，会将obj1和obj2的所有属性合并，并返回新的对象。

手写测试

<template>
  <div id="app">
    <img alt="Vue logo" src="./assets/logo.png">
    <HelloWorld msg="Welcome to Your Vue.js App"/>
  </div>
</template>

<script>
import HelloWorld from './components/HelloWorld.vue'

export default {
  name: 'App',
  components: {
    HelloWorld
  },
  data() {
    return {
      obj1: {
        key1: 1,
        key2: 2,
        methods: {
          test() {
            console.log('test');
          }
        }
      }
    }
  },
  created() {
    const obj2 = {
      key2: '4',
      key3: 3,
      methods: {
        test2() {
          console.log('test2');
        },
        test3() {
          console.log('test3');
        }
      }
    };
    const newObj = Object.assign(this.obj1, obj2);
    console.log(newObj);
    newObj.methods.test2();
    newObj.methods.test();
  },
}
</script>

<style>
#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

运行效果

注意

obj2.key2会覆盖掉obj1.key2的值，并且obj2.methods也会覆盖obj1.methods

思考

多个obj合并会如何？

const obj2 = {
      key2: '4',
      key3: 3,
      methods: {
        test2() {
          console.log('test2');
        },
        test3() {
          console.log('test3');
        }
      }
    };
    const obj3 = {
      key3: 99
    };
    const newObj = Object.assign(this.obj1, obj2, obj3);
    console.log(newObj);
    newObj.methods.test2();
    newObj.methods.test();

方法传入多个对象参数时，始终以最后的key3为最终有效值

使用Object.assign方法动态合并的对象与vue实例的响应式关系

<template>
  <div id="app">
    <img alt="Vue logo" src="./assets/logo.png">
    <span>{{ newObj.key3 }}</span>
    <HelloWorld msg="Welcome to Your Vue.js App"/>
  </div>
</template>

<script>
import HelloWorld from './components/HelloWorld.vue'

export default {
  name: 'App',
  components: {
    HelloWorld
  },
  data() {
    return {
      obj1: {
        key1: 1,
        key2: 2,
        methods: {
          test() {
            console.log('test');
          }
        }
      },
      newObj: null
    }
  },
  created() {
    const obj2 = {
      key2: '4',
      key3: 3,
      methods: {
        test2() {
          console.log('test2');
        },
        test3() {
          console.log('test3');
        }
      }
    };
    const obj3 = {
      key3: 99
    };
    this.newObj = Object.assign(this.obj1, obj2, obj3);
  },
}
</script>

<style>
#app {
  font-family: Avenir, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-align: center;
  color: #2c3e50;
  margin-top: 60px;
}
</style>

可以看到，初始化时data中的响应式数据里并没有key3键，但是使用assign方法后续加上的key3属性仍然正常显示在页面，所以该属性动态添加后是响应式的，并没有深度响应的问题。