Uncaught TypeError: Cannot read property 'options' of null - some of the code work

问题

I want to read the user's choice by the function:

    var e = document.getElementById("Trip_Type");
    var Trip_Type = e.options[e.selectedIndex].value;
    var i = document.getElementById("Trip_Population");
    var Trip_Population= i.options[i.selectedIndex].value;
    var j = document.getElementById("Trip_Duration");
    var Trip_Duration= j.options[j.selectedIndex].value;

The option Trip_Population and Trip_type is varchar and chosen from a drop down list:

<select id = "Trip_Population" style="width: 120px">
<option value="1">1</option>
<option value="2">2</option>
<option value="3">3</option>
<option value="4">4</option>
</select>

The Trip_Duration is float and chosen from free text input:

<input name="Trip_Duration" style="width: 117px" type="text"></strong></td>

After submitting the information I want a pop-up window with transferring information to the next page:

 var myWindow = window.open("Tripdet.php?Trip_Type="+Trip_Type+"&Trip_Population="+Trip_Population+"&Trip_Duration="+Trip_Duration, "", "width=400, height=200");

The pop-up not showing up and recive a error on the console on the Trip_Duration (if I remove it from the code it's working): Uncaught TypeError: Cannot read property 'options' of null

Thanks in advanced

回答1:

input tag does not have options. Just retrieve the value:

var Trip_Duration= j.value;

and as Phil pointed out, input is missing id

<input id="Trip_Duration" name="Trip_Duration" style="width: 117px" type="text">

来源：https://stackoverflow.com/questions/36754134/uncaught-typeerror-cannot-read-property-options-of-null-some-of-the-code-wo

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javascript

php

getelementbyid