jQuery：为什么这个小功能不起作用？

Question

it's supposed to add a number to the right of the LI, so the first LI would prepend the number 1, the second LI would prepend 2, etc.

also, are i = i+1; and i++; the same? if not, what's the difference?

http://jsfiddle.net/nicktheandroid/U8byW/9/

Answer 1

This line is the problem:

$(this).append("<span class="commentnumber"> #' i '</span>");

Use this instead:

$(this).append("<span class='commentnumber'> #" + i + "</span>");

Note that the string delimiters now match and the use of + to concatenate the strings.

When updating your code, it works - http://jsfiddle.net/U8byW/14/

---

And yes, i = i + 1; is the same as i++ for a single line statement.

Answer 2

You have some very broken and messed up simple and double quotes in your code, not to mention that you are trying to modify the i variable over which you are looping which is not a good thing. Try like this:

$('li').each(function (index) {
    $(this).append(
        $('<span/>').addClass('commentnumber').text('#' + (index + 1))
    );
});

or if you prefer (but be careful with the simple and double quotes):

$('li').each(function (index) {
    $(this).append('<span class="commentnumber">#' + (index + 1) + '</span>');
});

And demo here .

Answer 3

Try this solution: http://jsfiddle.net/U8byW/10/

The problems you had with yours were:

• When you said class="commentnumber" , you were breaking the JS strings, causing an error ( Uncaught SyntaxError: Unexpected identifier )
• You don't need to increment i at all: jQuery handles that for you. But to answer your question, i = i + 1 and i++ are roughly the same thing, yes. The difference is that i = i + 1 returns the new value (with 1 added to it) while i++ returns the old value and then increments it by one. You can also use i += 1 or ++i . All of those are rough equivalents.
• JavaScript does not format strings or insert variables inside of strings for you automatically like PHP or other languages. You have to concatenate the strings to insert variables. I've done that for you in the updated link above. Note that the string concatenation operator ( + ) is the same as the addition operator ( + ), unlike some languages (eg, PHP, where concatenation is . instead).

Hope this helps.

Edit: I realized why you were incrementing i : to have the lines start at 1 instead of 0. Ignore me saying you don't need to increment it. I wasn't thinking straight.