在 if 语句中将变量值作为条件传递

Question

我正在编写脚本，我想在 if 语句中将值作为条件传递，但它被视为字符串。我不明白为什么这个值被识别为字符串。我需要直接从数组中提取信息吗？

//extracting date and preparing condition 
function dateArgument () {
var start = $("#start").val();
var end = $("#end").val();
var y;

if(start && end){
    y = ' && arr[i].created.substring(0,10) >= '+start+' && arr[i].created.substring(0,10) <= '+end;
} else {
    y = '';
}
return y;
};

// Using Condition
function count (arr, nameVar, valueVar){
var x = 0;
// Preparing condition 
var contd = '$.trim(arr[i][nameVar]) == valueVar'+dateArgument();
console.log(contd);
var start = $("#start").val(); 
var end = $("#end").val();

for (i=0; i < arr.length; i++){
    // using prepared condition
             if (contd) {
        x++;
    }
}
return x;
};

// using prepared condition
function mapData (){
  $.ajax({
url:'http://192.168.2.20:8020'+partUrl('province')+partUrl('activity')+partUrl('priority')+partUrl('status'),
type: 'GET',
dataType: 'json',
success: function (data){
    //Using code here
    console.log(count(data,'priority','HighclearLayers();
    createPins(data);
    //summaryValues(data);
    }   
})
};

Answer 1

很简单。您不能使用字符串作为条件。如果确实需要，请使用 eval()。但请记住，eval 是邪恶的！

if (eval(contd)) {
  x++;
}

更好的解决方案：使用真实条件而不是字符串条件

if(start && end){
    //solve the first part of your condition here
    //this will return a boolean
    y = arr[i].created.substring(0,10) >= start && arr[i].created.substring(0,10) <= end;
} else {
    y = true;
}

//later prepare the condition it like this
//this will also return a boolean
var contd = $.trim(arr[i][nameVar]) == valueVar && dateArgument();

Answer 2

I am not getting why this value is recognized as string

确实是String，改成function以后调用

var contd = (i) => $.trim(arr[i][nameVar]) == valueVar && dateArgument(i);

并将其用作

 if ( contd(i) )

也把dateArgument改成

function dateArgument () 
{
    var start = $("#start").val();
    var end = $("#end").val();
    var y = () => true;

    if(start && end){
        y = (i) => arr[i].created.substring(0,10) >= start && arr[i].created.substring(0,10) <= end;
    } 
    return y;    
};

在 if 语句中将变量值作为条件传递

Passing variable value as condition in if statement

javascript

ajax

jquery

jquery-events