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Two var as true in an IF statement

I am trying to figure out how I can use those two vars:
var s = document.getElementById('styledselect1');
var d = document.getElementById('styledselect2');
and check with an if statement if both of them are equal to a certain number, like below:
if (s.value == 0 and d.value == 5)
How can I declare this and between these two values?
styledselect1 and styledselect2 are select options..

Just use && instead of and.
if (s.value() == 0 && d.value() == 5)
There are more "logical operators" than just &&. For example, there is || (or) that would only return true if at least one statement is true, ^ that would only be true if exactly one of the statements is true. Also, there is ! (in front of a statement) that inverts the statement(makes true to false and false to true.
If value() is actually a number, I would suggest you to use === as it will be false for the same string.

what is the issue in this javascript short circuit assignment

The following javascript code is getting giving undefined as the final output. But as far as I know the OR ' || ' operator will stop the evaluation as soon as it gets "true". But in this block of code it is trying to evaluate the remaining conditions even though it gets true on the first expression.
field = {
ipaddr: "0.0.0.0",
nodePresentInTopo: false
}
var bestName = field.ipaddr || (field.ip6addr && field.ip6addr != '::') ? field.ip6addr : undefined || field.sysid;
Here bestName always evalueavtes to undefined but why? As it is getting the value at field.ipaddr i.e 0.0.0.0
Please explain the logic.

In one word: operator precedence.
Yes, || short-circuits and doesn't evaluate the second half of the expression used as condition in the ternary operator.
field.ipaddr || (field.ip6addr && field.ip6addr != '::') ? .. : ..
Evaluates to:
'0.0.0.0' ? .. : ..
Which evaluates to true and then evaluates the true branch of the ternary operator:
field.ip6addr
If you want a different logical grouping, use parentheses:
field.ipaddr || (.. ? .. : ..);

I'm assuming you know that you've written field.ipaddr instead of fields.ipaddr. Probably for testing purposes. If the last part of the expression is your problem, write it like so:
(undefined || fields.sysid);

I don't think so is there any property with name ip6addr in current object?
var bestName = (field.ipaddr || (field.ip6addr && field.ip6addr != '::') ? field.ipaddr : undefined || field.sysid);
undefined
Either you should add ip6addr in current object or replace with appropriate property

JavaScript: When the `condition` portion of a `ternary` or `if` statement does not include `===` or `>=`

In the condition portion of the following ternary statement, does playlist.length equal playlist.length >= 1 ?
var playlist = ["video1", "video2", "video3", "video4", "video5"];
// some code here
alert ((playlist.length) ?
playlist.length + "video(s) remain in the playlist: " + playlist.join (", ") + "."
: "No videos remain in the playlist");
Likewise, in the following snippet of code, does ! playlist.length equal playlist.length === 0 ?
alert ((! playlist.length) ?
"No videos in the playlist."
: playlist.length + " video(s) remain in the playlist: " + playlist.join(", ") + ".");
This is the first time I've seen an example where the condition portion of a ternary or if statement does not include such a notation as === or >=. So I'm not sure how to interpret this.

0 is implicitly converted to false in boolean comparisons in JavaScript. So when the length is 0, that is false. Conversely, any other number is implicitly converted to true in boolean comparisons in JavaScript. So when the length is anything but 0 it is true.
An easy test is to use !! to see the "truthy" value
!!1 === true
!!0 === false
!!6 === true

The part to the left of the ? is simply evaluated for "truthiness". The value 0 is "falsy" so evaluates as false for the purposes of the test. Numeric values other than 0 are "truish" and therefore for this purpose evaluate to true.
All other behaviors of the ternary are the same.
The === and !== simply add the additional constraint that the L-value and R-value must also be the same type.

The two are very similar: !playlist.length and playlist.length === 0.
However, they are not exacty the same. In fact, here:
var playlist1 = [];
var playlist2 = {};
!playlist1.length // true
!playlist2.length // true
playlist1.length === 0 // true
playlist1.length === 0 // false
In that sense !playlist.length also can be used on all kinds of objects, not just arrays.
In any case, when using this on an array, it is a way to check if the array is empty, and works as you have suggested, the same as playlist.length === 0.

In javascript 0 equals false, and any other number value equals true, but if you use === it compare value types too.

how do i make this javascript logic + syntax (very simple)

Why I am getting true all the time?
var _template_id = "";
if (_template_id != '0' || _template_id!="") {
alert("true")
}else{
alert("false")
}
or even if i set _template_id="0", it still turns out as true...

Because you're asking if _template_id isn't equal to "0" OR isn't equal to "". One of those will always be true.
Proof: Given your statement of (_template_id != '0' || _template_id!=""), let's suppose that the first part is false. Therefore _template_id == '0' is true, and hence _template_id != "" is true, so overall the statement evaluates to true.
If, on the other hand, the first part is true, then clearly the whole thing evaluates to true again.
Therefore, the statement is always true.

You want && not ||.
It must always be true because "0" != "", so one or the other is always true.

a != b || a != c is always true when b and c are different.
What you want here is probably to use
if (!(_template_id == '0' || _template_id =="")) {
alert("true")
Then if you set _template_id="0" you would get false as desired.

You probably want
!(_template_id == '0' || _template_id == "")
If _template_id is neither 0 nor ''.
This is equivalent (thanks to De Morgan's laws) to:
_template_id != '0' && _template_id != ""

Where are you trying to change the value of _template_id ? I will always be true if you assign "" and then ask if its '0' or "" then true.

You are logically going wrong.
Either use == and ¦¦
Or
Use != and &&
It will result the same in both cases and your condition will be true as well.

Logical && operator

Having an unpredicted outcome using the && logical operator. If I link more than 2 expressions, the if clause fails. Is there some limit to the number of expressions that can be concatenated using &&?
if (tTellerProN.checked && tCareProN.checked && tSalesProN.checked) {
$(flListEmpty).empty();
$(flListEmpty).append($('<option></option>').val(0).html("Select Role"));
$('.fl_list1 .list4').each(function (index) {
$(flListEmpty).append($('<option> </option>').val(index).html($(this).text()));
})
}

&& is not a jQuery operator, it is Javascript. jQuery is a library that builds on Javascript.
I'm not sure what the ** is in your IF statment but this code works:
var x = true;
var y = true;
var z = true;
alert(x && y && z); // true
alert(x && y && !z); // false
I would alert the values of your 3 .checked parameters and make sure they are being set as you expected.

No, there is no limit. Your expression requires that all three checked values are true, otherwise it will return false. One of them must be false (or not true), that's why your if is failing.
For the record: && is part of the javascript language, not the jQuery library.

No, there is no limit.
However looking at your code (what little there is of it and with such descriptive variable names used), I would venture a guess that you actually mean ||, not &&.

i made a test case here with both && and ||: http://jsfiddle.net/VcmCM/