JQuery, selectors/filters/performance optimization

1. Browser introduction:

1. The jquery object is an array-like object. The array-like object has length and can be passed Index access, if the array-like object is not added manually, the methods of the array object are not available.

2. The length of an array will automatically grow when adding elements, but a class array will not.

3. Class arrays can be converted into arrays through the slice method:

##

Array.prototype.slice.call(a);

1. JQuery basic selector:

1. ID selector

2. Class selector

3. Descendant selector

4. Attribute selector

5. a[href!="http://www.baidu.com"], a new method in jquery, selects all elements that are not equal to Baidu URL.

1. JQuery Filter/Filter:

• lang(language) ：Select elements in the specified language

• not(selector) ：Select all elements that are not the specified elements

• root                                                                                                                                                                                                                                                  Contains OPACITY, does not include HIDDEN elements, excluding elements that are not displayed in the position

• Visible: Just opposite to Hidden

## Header ：Select the title element
animated ：Select all elements that are performing animation effects
• ##：empty ：Select the content Empty elements

• : contains(text) : Select elements to filter text

• ：parent ：Select the parent element
• :first-child

• :last-child

##first-of-type : Select the first one with the same type: li:first-of-type

• last-of-type

• nth-child() : Counting from 1

• nth-last-child()

• nth-of-type()

• ##nth-last-of-type()

• only-child

• only-of-type

• ##:checked : Select the selected

• :disabled : Select and disable

• :enabled : All except disabled ones can be selected

: focus : generally not used directly, wait until the form is loaded before using
: button : not only selects the button, but also selects the type of button
:checkbox ：Select all multi-select boxes
:file ：Select the file input box
:image ：Select the type of image Element
:input : Select all form elements
:password
:radio : Select the radio button
:reset ：The selected type is reset,
:selected ：Select all selected states
:submit : The selected type is submit, and some browsers will also select button
:text : The selected type is text, and ## with no type set will also be selected.
• #:first

• :last

• :even

• :eq(n) : equal to n

• ##:gt(n) : greater than n

• :lt(n) : less than n

Position filter:
Form Filter
Child Element Filter
Content Filter

1. ## Other filters

2. Custom selector

1. Performance optimization of JQuery selector:

1. Try to use selectors available in CSS

2. Avoid over-constraints

3. Try to start with ID

4. Let the selector have more features on the right side

5. Avoid using global selectors

6. Cache selector results

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