vue - 왜 하위 구성 요소의 데이터 옵션이 함수여야 합니까?

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 6     "</span><span style="color:#800000;">../../vue.js</span><span style="color:#800000;">"</span>>
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"app">
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<span style="color:#008080;">40</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> data ， ，
</span><span style="color:#008080;">41</span>     <span style="color:#008000;">//</span><span style="color:#008000;">  ， 
</span><span style="color:#008080;">42</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> data 
</span><span style="color:#008080;">43</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> let data = {
</span><span style="color:#008080;">44</span>     <span style="color:#008000;">//</span><span style="color:#008000;">     counter:0
</span><span style="color:#008080;">45</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> };
</span><span style="color:#008080;">46</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> data(){
</span><span style="color:#008080;">47</span>     <span style="color:#008000;">//</span><span style="color:#008000;">     return data;
</span><span style="color:#008080;">48</span>     <span style="color:#008000;">//</span><span style="color:#008000;"> }
</span><span style="color:#008080;">49</span> 
<span style="color:#008080;">50</span>     <span style="color:#008000;">//</span><span style="color:#008000;">2. </span>
<span style="color:#008080;">51</span>     Vue.component(<span style="color:#800000;">'</span><span style="color:#800000;">my-btn</span><span style="color:#800000;">'</span><span style="color:#000000;">,{
</span><span style="color:#008080;">52</span>         template:<span style="color:#800000;">'</span><span style="color:#800000;">#my_btn</span><span style="color:#800000;">'</span><span style="color:#000000;">,
</span><span style="color:#008080;">53</span> <span style="color:#000000;">        data(){
</span><span style="color:#008080;">54</span>              <span style="color:#0000ff;">return</span><span style="color:#000000;">{
</span><span style="color:#008080;">55</span>                  counter:<span style="color:#800080;">0</span>  <span style="color:#008000;">//</span><span style="color:#008000;"> ， counter ， data ，</span>
<span style="color:#008080;">56</span> <span style="color:#000000;">             }
</span><span style="color:#008080;">57</span> <span style="color:#000000;">        }
</span><span style="color:#008080;">58</span> <span style="color:#000000;">    })
</span><span style="color:#008080;">59</span> 
<span style="color:#008080;">60</span> 
<span style="color:#008080;">61</span>     <span style="color:#0000ff;">var</span> vm = <span style="color:#0000ff;">new</span><span style="color:#000000;"> Vue({
</span><span style="color:#008080;">62</span>         el:<span style="color:#800000;">'</span><span style="color:#800000;">#app</span><span style="color:#800000;">'</span><span style="color:#000000;">,
</span><span style="color:#008080;">63</span> <span style="color:#000000;">        data:{}
</span><span style="color:#008080;">64</span> <span style="color:#000000;">    })
</span><span style="color:#008080;">65</span> 
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