Javascript，并在括号符号中使用变量而不是字符串

Question

I have a PHP script that takes a text list with a variable number of questions and generates HTML form code that looks like this.

What did you think of X?<br />
<input type="hidden" name="$survey[0][0]" value="What did you think of X?">
<input type="radio" name="$survey[0][1]" value="1">Didn't like it.
<input type="radio" name="$survey[0][1]" value="2">I was indifferent.
<input type="radio" name="$survey[0][1]" value="3">Liked it.

$survey[n][0] is the question, $survey[n][1] is the answer, and n is the variable number of questions.

To validate using Javascript, I have a loop that loops through the questions, and a loop inside it that makes sure each question has an answer. My problem is referencing the elements with [] in their names. Here's what I think is the relevant part of my code.

var formElements = document.forms["form"].elements;
var groupCount = document.getElementsByTagName("li").length;
var groupNdx = 0;
var groupName = "";
var btnCount = 0;
while (groupNdx < groupCount) {
  groupName = "'$survey[" + groupNdx + "][1]'";
  btnCount = formElements[groupName].length;

That last line doesn't work because formElements[groupName] is "undefined." formElements['$survey[3][1]'] works just fine, but that hardcodes the element's name, and I'd need to repeat the code for each question, and worse, it's a variable number of questions.

As I was typing, the Similar Questions sidebar suggested I read Why aren't variable names converted to strings when using bracket notation in javascript? , so now I that's just how it is in Javascript.

But then what workaround would you suggest? I could just forget about validating with Javascript since I also validate the form with PHP, but I understand it's good practice to validate forms at both the client and server sides. Thanks for your help!

Answer 1

You have an extra set of single quotes that you shouldn't here:

groupName = "'$survey[" + groupNdx + "][1]'";

That adds single quotes into the key itself. Change that to:

groupName = "$survey[" + groupNdx + "][1]";

Notice that x["'key'"] is a different from x['key'] in Javascript. The first has a key of 'key' (including the quotes) while the second has just the string: key