Learn Jquery with JQuery API Part 3 Filtering_jquery

1. Filter
eq (index) Look at this function and the basic one: eq seems to be the same (actually it is the same)
For example, we have to select, then we can use $(“div”).eq(1) or $(“div:eq(1)”)
to select the second div, the effect is the same

hasClass(class) is used to determine whether the current element contains a class. This is the same as is(“.” class). Let’s take a look at what the is() function is used for. It uses an expression. To check the currently selected set of elements and return true if at least one element matches the given expression. The parameters in is(expr) are the parameters of the selector.

filter(expr) is used to select a set of elements with matching expressions. This is somewhat similar to is, except that is is the returned bool type and is used for judgment. filter is used to narrow the range. filter The parameter in can be a function, and the return value of the function is of bool type. When the return value is true, the node is retained. In fact, it is to make a loop through the objects and then delete the unnecessary ones. For example, if there is

asdf

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we choose the one with class aa and change his text into a paragraph of text
$("p").filter(function() { return $( this).hasClass("aa") }).text("selected thing")

not(txpr) is used to delete matching elements. This is the same as the previous one: not()
slice(start,[end]) selects a segment starting from start to end and ending if there is no end
$("p").slice(0, 1), I always feel that the second part of this function It would be better if the variable should be num. From which one to start, select the first num.

2 Search
add(expr) Add the object that matches the expression to the original object. This is a bit like a multi-selector such as $("#id,.cs" )
It can also be written as $("#id").add(".cs") with the same effect
Children([expr]) gets the set of all child elements
Contents() finds all matching elements child nodes. If it is an iframe, search the content of the document. This can be easily used to change the content inside the iframe, such as a text editor. .
find(expr) searches for content that matches the specified expression. This can also be implemented using a selector. For example, $("ul li") can be written as $("ul").find("li")
next(expr) searches for the element immediately following among the sibling elements. This is the selector form of a b. For example, if we want to select $("div p") followed by a div followed by a p tag, of course we can also use $("div") .next("p")
nextAll() searches for all subsequent sibling elements. This is the same as a~b. $("div~p") and $("div").nextAll("p") are The same
Prev([expr]) gets the previous element of the immediately adjacent sibling element, which is exactly the opposite of next()
PrevAll([expr]) gets all the previous elements, which is exactly the opposite of nextAll()
Siblings([expr]) This function should be the sum of nextAll() and prevAll()

offsetParent() returns the parent node of the first element. Why is it the first element? This is done with JavaScript The implementation is Parent(), but we use jquery and operate jquery objects. Many tutorials emphasize that we need to distinguish between JQuery objects and JS objects. In fact, the Jquery object is an array array, which requires us to pay attention to the operation. When you want to take out the value of the array, you want to use the first and last price index [0] to get the first object.
Parent(expr) gets the parent element contained by all elements. We already know that the jquery object is an array, so it may contain multiple nodes. Then we need to find the common parent node of these multiple nodes, and It is to find a node that can contain them all. Just like there are two people, one is from Hubei and the other is from Henan. You want to find his superior, that is, they are both from China. Of course, you can also fill in a parameter parent (Hubei), then the final node we get is Hubei.

3 Concatenation
There are only two functions in concatenation andSelf() and end()
andSelf() adds the previously selected element to the current element, this explanation It's a bit convoluted to read. Here we should mention Jquery’s chain operation. For example, if you select China-Hubei, you will get the Hubei node, and then you use andSelf() to add China. This will be very useful if you want to operate on elements that you have not filtered before.
end() goes back to the last "destructive" operation. So what is destructive? It is to perform the next operation on a collection
For example, next() we mentioned earlier, here we go. We now know why the operation we can complete with $("div p") must be written as $("div").next("p").