在用javascript再次聲明它之前清除或刪除變量

Question

我對JavaScript很新穎，並且正在搞一些數學。我目前有：

<input disabled="disabled" type="text" id="backer-prediction-answer" width="100" value="" /> 

<FORM> 
    <INPUT type="button" value="Apply" name="button1" onclick="apply()"> 
</FORM> 

<script> 
var backerPrediction1 = document.getElementById("backer-prediction-1").value; 
var backerPrediction2 = document.getElementById("backer-prediction-2").value; 
var backerPrediction3 = document.getElementById("backer-prediction-3").value; 
var backerPrediction4 = document.getElementById("backer-prediction-4").value; 

function apply(){ 
    var backers = parseInt(backerPrediction1,10) + parseInt(backerPrediction2,10); 
    document.getElementById("backer-prediction-answer").value = (backers); 
} 
</script> 

我想能夠擊中申請並重新計算。在再次聲明之前是否需要刪除變量？如果是這樣，我該怎麼做？

Answer 1

移動變量backerPredictionX裏面的功能，讓他們進行評估，每次應用（）

<script> 

function apply(){ 
    var backerPrediction1 = document.getElementById("backer-prediction-1").value; 
    var backerPrediction2 = document.getElementById("backer-prediction-2").value; 

    var backers = parseInt(backerPrediction1,10) + parseInt(backerPrediction2,10); 
    document.getElementById("backer-prediction-answer").value = (backers); 
} 
</script> 

---

使用jQuery（代碼未驗證）：

function apply(){ 
    var backerPrediction1 = $("#backer-prediction-1").val(); 
    var backerPrediction2 = $("#backer-prediction-2").val(); 

    var backers = parseInt(backerPrediction1,10) + parseInt(backerPrediction2,10); 
    $("#backer-prediction-answer").val(backers); 
}