为什么连接字符串返回未定义

如何解决为什么连接字符串返回未定义

我正在进行 API 调用，当我将一些值连接到一个变量时，它工作正常，但由于某些原因，在句子的开头它具有“未定义”。我不明白为什么。这是我的代码

Model: "model_33"
__________________________________________________________________________________________________
Layer (type)                    Output Shape         Param #     Connected to                     
==================================================================================================
observations (InputLayer)       [(None,84,4)]  0                                            
__________________________________________________________________________________________________
layer1 (Conv2D)                 (None,20,32)   8224        observations[0][0]               
__________________________________________________________________________________________________
layer2 (Conv2D)                 (None,9,64)     32832       layer1[0][0]                     
__________________________________________________________________________________________________
layer3 (Conv2D)                 (None,7,64)     36928       layer2[0][0]                     
__________________________________________________________________________________________________
layer4 (Flatten)                (None,3136)         0           layer3[0][0]                     
__________________________________________________________________________________________________
agent_indicator (InputLayer)    [(None,2)]          0                                            
__________________________________________________________________________________________________
concatenate_18 (Concatenate)    (None,3138)         0           layer4[0][0]                     
                                                                 agent_indicator[0][0]            
__________________________________________________________________________________________________
layer5 (Dense)                  (None,512)          1607168     concatenate_18[0][0]             
__________________________________________________________________________________________________
gamma_q_layer0 (Dense)          (None,6)            3078        layer5[0][0]                     
__________________________________________________________________________________________________
gamma_q_layer1 (Dense)          (None,6)            3078        layer5[0][0]                     
__________________________________________________________________________________________________
gamma_q_layer2 (Dense)          (None,6)            3078        layer5[0][0]                     
__________________________________________________________________________________________________
concatenate_19 (Concatenate)    (None,18)           0           gamma_q_layer0[0][0]             
                                                                 gamma_q_layer1[0][0]             
                                                                 gamma_q_layer2[0][0]             
==================================================================================================
Total params: 1,694,386
Trainable params: 1,386
Non-trainable params: 0
__________________________________________________________________________________________________
None

const APIKEY = 'ajhy1e4j9rudm4lces756';
const URL = `https://api.lunarcrush.com/v2?data=assets&key=${APIKEY}&symbol=DOGE&data_points=365&interval=day`;

const text = document.getElementById('price');
let textToPutIn;
let callTheAPI = () => {
    const xhr = new XMLHttpRequest();
    xhr.open('GET',URL,true);
    xhr.onload = function() {
        if(this.status === 200) {
            let response = JSON.parse(this.responseText).data[0];
            console.log(response);
            let percent = (percent_change) => percent_change < 0 ? 'red' : 'green';
            
            textToPutIn += `${response.symbol}'s Current Price: <b>$${response.price}</b>
            
            Price in Bitcoin: <b>${response.price_btc}₿</b>
            
            ${response.symbol}'s Rank for 24 hours - <b>#${response.volume_24h_rank}</b>
            
        Percent change during 24h: <span style="color: ${percent(response.percent_change_24h)};">${response.percent_change_24h}%</span>    Difference during 7 days: <span id='7day' style="color: ${percent(response.percent_change_7d)};">${response.percent_change_7d}%</span>`;
        }
    text.innerHTML = textToPutIn;
    }
    xhr.send();
}

callTheAPI();

如果你运行代码，它会在“DOGE”前面返回 undefined。

P.S 我知道这是调用 API 的一种旧方式。提前致谢！