Develop Reference

Check if elements are part of wrapper [duplicate]

How can I check if one DOM element is a child of another DOM element? Are there any built in methods for this? For example, something like:
if (element1.hasDescendant(element2))
or
if (element2.hasParent(element1))
If not then any ideas how to do this? It also needs to be cross browser. I should also mention that the child could be nested many levels below the parent.

You should use Node.contains, since it's now standard and available in all browsers.
https://developer.mozilla.org/en-US/docs/Web/API/Node.contains

Update: There's now a native way to achieve this. Node.contains(). Mentioned in comment and below answers as well.
Old answer:
Using the parentNode property should work. It's also pretty safe from a cross-browser standpoint. If the relationship is known to be one level deep, you could check it simply:
if (element2.parentNode == element1) { ... }
If the the child can be nested arbitrarily deep inside the parent, you could use a function similar to the following to test for the relationship:
function isDescendant(parent, child) {
var node = child.parentNode;
while (node != null) {
if (node == parent) {
return true;
}
node = node.parentNode;
}
return false;
}

I just had to share 'mine'.
Although conceptually the same as Asaph's answer (benefiting from the same cross-browser compatibility, even IE6), it is a lot smaller and comes in handy when size is at a premium and/or when it is not needed so often.
function childOf(/*child node*/c, /*parent node*/p){ //returns boolean
while((c=c.parentNode)&&c!==p);
return !!c;
}
..or as one-liner (just 64 chars!):
function childOf(c,p){while((c=c.parentNode)&&c!==p);return !!c}
and jsfiddle here.
Usage:
childOf(child, parent) returns boolean true|false.
Explanation:
while evaluates as long as the while-condition evaluates to true.
The && (AND) operator returns this boolean true/false after evaluating the left-hand side and the right-hand side, but only if the left-hand side was true (left-hand && right-hand).
The left-hand side (of &&) is: (c=c.parentNode).
This will first assign the parentNode of c to c and then the AND operator will evaluate the resulting c as a boolean.
Since parentNode returns null if there is no parent left and null is converted to false, the while-loop will correctly stop when there are no more parents.
The right-hand side (of &&) is: c!==p.
The !== comparison operator is 'not exactly equal to'. So if the child's parent isn't the parent (you specified) it evaluates to true, but if the child's parent is the parent then it evaluates to false.
So if c!==p evaluates to false, then the && operator returns false as the while-condition and the while-loop stops. (Note there is no need for a while-body and the closing ; semicolon is required.)
So when the while-loop ends, c is either a node (not null) when it found a parent OR it is null (when the loop ran through to the end without finding a match).
Thus we simply return that fact (converted as boolean value, instead of the node) with: return !!c;: the ! (NOT operator) inverts a boolean value (true becomes false and vice-versa).
!c converts c (node or null) to a boolean before it can invert that value. So adding a second ! (!!c) converts this false back to true (which is why a double !! is often used to 'convert anything to boolean').
Extra:
The function's body/payload is so small that, depending on case (like when it is not used often and appears just once in the code), one could even omit the function (wrapping) and just use the while-loop:
var a=document.getElementById('child'),
b=document.getElementById('parent'),
c;
c=a; while((c=c.parentNode)&&c!==b); //c=!!c;
if(!!c){ //`if(c)` if `c=!!c;` was used after while-loop above
//do stuff
}
instead of:
var a=document.getElementById('child'),
b=document.getElementById('parent'),
c;
function childOf(c,p){while((c=c.parentNode)&&c!==p);return !!c}
c=childOf(a, b);
if(c){
//do stuff
}

Another solution that wasn't mentioned:
Example Here
var parent = document.querySelector('.parent');
if (parent.querySelector('.child') !== null) {
// .. it's a child
}
It doesn't matter whether the element is a direct child, it will work at any depth.
Alternatively, using the .contains() method:
Example Here
var parent = document.querySelector('.parent'),
child = document.querySelector('.child');
if (parent.contains(child)) {
// .. it's a child
}

You can use the contains method
var result = parent.contains(child);
or you can try to use compareDocumentPosition()
var result = nodeA.compareDocumentPosition(nodeB);
The last one is more powerful: it return a bitmask as result.

Take a look at Node#compareDocumentPosition.
function isDescendant(ancestor,descendant){
return ancestor.compareDocumentPosition(descendant) &
Node.DOCUMENT_POSITION_CONTAINS;
}
function isAncestor(descendant,ancestor){
return descendant.compareDocumentPosition(ancestor) &
Node.DOCUMENT_POSITION_CONTAINED_BY;
}
Other relationships include DOCUMENT_POSITION_DISCONNECTED, DOCUMENT_POSITION_PRECEDING, and DOCUMENT_POSITION_FOLLOWING.
Not supported in IE<=8.

I came across a wonderful piece of code to check whether or not an element is a child of another element. I have to use this because IE doesn't support the .contains element method. Hope this will help others as well.
Below is the function:
function isChildOf(childObject, containerObject) {
var returnValue = false;
var currentObject;
if (typeof containerObject === 'string') {
containerObject = document.getElementById(containerObject);
}
if (typeof childObject === 'string') {
childObject = document.getElementById(childObject);
}
currentObject = childObject.parentNode;
while (currentObject !== undefined) {
if (currentObject === document.body) {
break;
}
if (currentObject.id == containerObject.id) {
returnValue = true;
break;
}
// Move up the hierarchy
currentObject = currentObject.parentNode;
}
return returnValue;
}

Consider using closest('.selector')
It returns null if neither element nor any of its ancestors matches the selector. Alternatively returns the element which was found

try this one:
x = document.getElementById("td35");
if (x.childElementCount > 0) {
x = document.getElementById("LastRow");
x.style.display = "block";
}
else {
x = document.getElementById("LastRow");
x.style.display = "none";
}

TL;DR: a library
I advise using something like dom-helpers, written by the react team as a regular JS lib.
In their contains implementation you will see a Node#contains based implementation with a Node#compareDocumentPosition fallback.
Support for very old browsers e.g. IE <9 would not be given, which I find acceptable.
This answer incorporates the above ones, however I would advise against looping yourself.

javascript passing the result of a boolean comparison confusion

I've been working through some text book to learn web development and i've become confused on an example. The example creates a meter element and fills it with some attributes. There is then some javascript to check for browser support for the tag. The part where i'm confused is after the first expression returns either true or false for the support, shouldn't there be a check for if true or false was returned on the following if statement? also as an aside, when the create element builds the element does is give it default values, or grab values from an existing meter in the html.
The check for support is as follows.
var noMeterSupport = function(){
return(document.createElement('meter').max === undefined);
}
the next part that builds the meter if the support isn't found is below. This is where i become confused as it seems to take either value and continue without checking if it was true or false.
if (noMeterSupport()) {
var fakeMeter, fill, label, labelText, max, meter, value;
value = meter.attr("value");
meter = $("#pledge_goal");
max = meter.attr("max");
labelText = "$" + meter.val();
fakeMeter = $("<div></div>");
fakeMeter.addClass("meter");
label = $("<span>" + labelText + "</span>");
label.addClass("label");
fill = $("<div></div>");
fill.addClass("fill");
fill.css("width",(value / max * 100) + "%");
fill.append("<div style='clear:both;'><br></div>");
fakeMeter.append(fill);
fakeMeter.append(label);
meter.replaceWith(fakeMeter);
}

The body of the if is only executed if noMeterSupport() returns true. The condition in an if statement requires something "truthy", i.e. something that can be interpreted as true or false. Since the function returns a boolean value, that is sufficient. (See first Google hit for truthiness javascript, which is a good explanation.)
EDIT: Forgot about your second question. When a new element is created with document.createElement, it does indeed get default values. In your example, the default value of max for a <meter> is 1.

if (noMeterSupport()) { checks the return value. It means exactly the same as this:
var supported = noMeterSupport();
if(supported) {

I hope that I understand your question correctly and will try to answer it.
So you would expect something like this:
if (noMeterSupport() == true)
Actually, this is equivalent to this:
if (noMeterSupport())
And if you want to check false:
if (noMeterSupport() == false)
This is equivalent to:
if (!noMeterSupport())

This statement will make the function either return true or false:
return(document.createElement('meter').max === undefined)
basically it would be synonymous with writing:
if(document.createElement('meter').max === undefined) {
return true;
} else {
return false;
}
That makes the value of noMeterSupport() either true or false.

var noMeterSupport = function(){
return(document.createElement('meter').max === undefined);
}
noMeterSupport returns the result of the comparison document.createElement('meter').max === undefined.
The comparison will be either true or false, ok?
So, now, when you do
if (noMeterSupport()) { /*then do something*/}
is like saying
if (/*the result of noMeterSupport() is true*/) {/*then do something*/}
So, this if statement will only run if noMeterSupport returns true

var noMeterSupport = function(){
return(document.createElement('meter').max === undefined);
}
This section of code is not actually doing the check, it is defining a function called noMeterSupport.
The code is not actually run until the function is called. It is called by adding () to the function name.
noMeterSupport()
Your if() statement is where it is being called as it the brackets.

You expect a boolean condition inside the if statement:
if(<boolean_condition>)
{
...
}
The noMeterSupport() is actually returning true or false, so the
if(noMeterSupport())
is converted to if(true) or if(false)
depending on the result of the document.createElement('meter').max === undefined evaluation.
You are receiving a boolean condition and the if statement works fine.

As a beginner, there's two points to quickly learn in programming :
The comparison operators == and === not only do the comparison, but returns in fact the result of this comparison (you can place it in var to test)
var bool = 1 === 2;
console.log(bool); // will print false
The test if(boolean === true) is equivalent to if(boolean), and the test if(boolean === false) is equivalent to if(!boolean)

Javascript, Comparing objects with indexOf

I am trying to compare a current object to an array of id's coming in. The basic idea is that if the object has the same idea as anything inside the recived ID array, then I would like to set a boolean of selected to true. I was pointed in the direction of using a for each with an indexOf inside to check against. Here is my Attempt -
angular.forEach($scope.applicationsHere, function(index) {
if(data.applications.indexOf(index.id){
index.selected = true;
}
});
So what I am tyring to do is check the applications here against the data.applications. If the applicationsHere has an object with .id that matches one of the numbers in data.applications (data.applications is just an array of ids like [1,2,3]), then set the .selected to equal true.
I do not believe I have this logic correct, if anyone could help correct me I would much appreciate it. Thanks for reading!

if(data.applications.indexOf(index.id){ // this is missing a parenthesis
This line has the following actual behavior (thanks #Pointy for clarifying all the options)
Not found (-1) = true
First Element (0) = false
Any other element (1 to n) = true
From your question, your expected output is:
Not found (-1) = false
Found (0 to n) = true
If you're attempting to use JS' 0 = false, anything else is true, then you can do:
angular.forEach($scope.applicationsHere, function(index) {
if(data.applications.indexOf(index.id) + 1) {
index.selected = true;
}
});
Or, even shorter:
angular.forEach($scope.applicationsHere, function(index) {
index.selected = (data.applications.indexOf(index.id) + 1);
});
That being said, I would still recommend doing an actual >= 0 check for indexOf. Coercing like this causes confusion for other people reading the code since you're using an index for a boolean output. You can use a ternary operator if you're looking for compactness too.
angular.forEach($scope.applicationsHere, function(index) {
index.selected = data.applications.indexOf(index.id) >= 0 ? true : false;
});

Greasemonkey testing if array element exists

I'm writing a script that adds labels to things on a page using an element from an array based on part of the link... so my array looks like this:
var componentList[9] = "Sunnyseed"
var componentList[10] = "Echoberry"
var componentList[11] = "Riverstone"
var componentList[13] = "Auraglass"
var componentList[14] = "Skypollen"
You'll notice there is no '12'... I want the label to be 'Unknown' when the array item doesn't exist. Now, I can't exactly test my solution since I can't cause the target page to throw me a 12... so I was hoping somebody would tell me whether this will do what I want or not...
var component = ""
if(typeof componentList[critterIDval] == 'undefined'){
component="Unknown"
}
else{
component=componentList[critterIDval]
}
This is obviously not the full script, but it should be the important stuff... I just want to know if that will make it say 'Unknown' when the critterIDval is 12 - since it could take years to come across the situation for testing.

You're pretty much there. You're using a single-equals sign in your comparison, so that will mess it up, and I'm not sure you can create a JS array like that, but aside from that, you're good.
Here is the test I ran for it:
var componentList = [];
componentList[9] = "Sunnyseed";
componentList[10] = "Echoberry";
componentList[11] = "Riverstone";
componentList[13] = "Auraglass";
componentList[14] = "Skypollen";
for (var critterIDval = 9; critterIDval < 15; critterIDval++) {
if (typeof componentList[critterIDval] == 'undefined') { // double equals here
component = "Unknown";
} else {
component = componentList[critterIDval];
}
console.log(component);
}

It looks fine.
Though if you are sure that the value will never be an empty string(like componentList[14] = '';) then you can try
var component = componentList[critterIDval] || 'Unknown'

I want the label to be 'Unknown' when the array item doesn't exist.
The typeof operator does not tell you if a property exists or not as it returns undefined when the property doesn't exist but also when it does exist and has been assigned a the value undefined or simply created but hasn't been assigned a value.
There are two primary ways to test for the existence of a property: the in operator, which also looks on the [[Prototype]] chain and the hasOwnProperty method of all Objects. So
if (componentList.hasOwnProperty(critterIDval)) {
component = "Unknown"
} else {
component = componentList[critterIDval]
}
which you could also write as:
component = componentList.hasOwnProperty(critterIDval)? componentList[critterIDval] : 'unknown';
PS. there are other methods, such as looking at Object.keys(componentList) and componentList.propertyIsEnumerable(critterIDval), but the above are the most common.
Edit
If your requirement is not just to test for property existence but to also test for a "truthy" value, then:
if (componentList[critterIDval])
may be sufficient and will return false where the value is '' (empty string), 0, false, NaN, undefined or null.
Maybe just testing for a non–empty string or number will do:
if (/.+/.test(componentList[critterIDval]))
but that returns true for NaN, null and so on. So you need to specify what you are actually testing for, otherwise you may get undesired results for some values.

If statement is not working properly

I'm trying to change the condition in which data is written to a table. I noticed a strange result when trying to change this: it seems WriteToTable function would runno matter what if condition I subjected it to. To test this I did the following:
var TestThis=0;
if (TestThis=1000){
WriteToTable(iPlaceDisplayNum, place.name, place.rating, xScoreFinal, iProspect, place.url, place.formatted_phone_number);
alert ('This alert should not be displaying.');
}
The function will still execute and the alert will be still be displayed when the script runs. I'm not sure why?
Here's the rest of the function, the problem is towards the bottom:
function printme(place, status) {
if (status == google.maps.places.PlacesServiceStatus.OK) {
if (typeof place.reviews !== 'undefined') {
var xScore = 0;
var xGlobal = 0;
for (var i = 0; i < place.reviews.length; i++) {
reviews = place.reviews[i];
for (var x = 0; x < reviews.aspects.length; x++) {
aspectr = reviews.aspects[x];
xScore += aspectr.rating;
xGlobal++;
}
}
var xScoreFinal = (xScore / xGlobal);
}
if (typeof xScoreFinal !== 'undefined') {
iPlaceDisplayNum++;
var iProspect;
if (xScoreFinal < 2.3) {
iProspect = 'Yes';
}
//Not sure what's going on here
var TestThis=0;
if (TestThis=1000){
WriteToTable(iPlaceDisplayNum, place.name, place.rating, xScoreFinal, iProspect, place.url, place.formatted_phone_number);
alert ('This alert should not be displaying.');
}
}
}
}

You are assigning a value to your variable in your if condition check. Your TestThis variable is being assigned value 1000, which will be true after being converted to boolean by JavaScript. That's why your function is being always executed. You can read more about the automatic type conversion here.
Now to fix your code, change this -
if (TestThis=1000)
to this -
if (TestThis == 1000)
or if you don't want automatic type conversion -
if (TestThis === 1000)
Sometimes people like to reverse the values in the comparison, in the following way -
if (1000 === TestThis)
This is called a Yoda Condition (yeah, named after the Grand Jedi Master Yoda) . The benefit is that in case someone mistakenly puts only a single equal, it will result in an error as you cannot assign anything to a constant. I have never used it personally though (and probably never will because I find it rather unconventional).

JavaScript allows you to assign a value in a conditional, so this TestThis=1000 results to 1000 and in a conditional statement positive numbers (actually anything not 0) result to an evaluation to true.
To make it a conditional, you should do TestThis===1000 (and you should almost always use the === over the == as the === forces an actual comparison of the two and doesn't try to convert one part of the conditional to equal the other.)
You can also do 1000 === TestThis (or conversly 1000 == TestThis) Some people say this is bad coding, because it's difficult to read. I'll leave that up to you to decide, but this absolutely won't allow you to accidentally assign a value in the conditional because you can't assign a value to 1000.

In the if statement, you're setting TestThis to 1000, rather than comparing it to 1000. The = operator returns the value that was set, which evaluates to true because it is not undefined, 0, or null. You simply need to use the == operator.
if(TestThis == 1000)

if (TestThis == 1000)
Change like this.
For comparing equality in if you must have ==

Change:
if (TestThis=1000)
To:
if (TestThis==1000)
You're actually assigning to TestThis which will return true and execute the conditional block.