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This article focuses on "what are the methods of javascript to achieve native ajax", interested friends may wish to take a look. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn "what are the ways to implement native ajax with javascript?"

1. What does the front end do?

The front end is to do IT system engineering, responsible for the design and construction of information system, including equipment, system, database, application system construction.

two。 Development process

Development process

For the specific development journey, please see Baidu brain Map-- A convenient thinking tool.

3. The core language of front-end development

HTML-- structure CSS-- style JS-- behavior

Hypertext is beyond text, can display text, pictures, video audio, and most importantly, can contain hyperlinks.

Markup language: when we put specific English words into our tags (single tag: double tag), our markup has a new semantics, and by the specification of tags with specific semantics, we can call it markup language.

When we put English words into the tag, we can call it a tag (single tag, double label).

The basic structure of HTML

Elements in head

Description

Defines the information of the document

Defines the title of the document

Defines the default link address for the page link label

Defines the relationship between a document and external resources

Defines the metadata in the HTML document

Defines the script file for the client

Defines the style file for the HTML document

1. The introduction of CSS

Inline style sheet

Inline style sheet

Internal style sheet

Write on the inside

Internal style sheet

External style sheet

Write it separately in a file and introduce it through link

Rel: the relationship between the currently introduced file and the file itself

Type: the encoding format of the currently imported file

Href: used to write where the external style is introduced

External style sheet

2. CSS selector

When we use inline styles, the CSS style can explicitly modify the label of the style we want to change. If we write the CSS style internally or externally, we need to use the CSS selector to select the tag we want to change the style.

There are three types of CSS selectors

Label signature selector div {width:100px; … }

A certain type of tag will be selected directly, and all of these tags will take effect.

Priority: type 1 selector. Div {width:100px; … }

When using the class selector, we need to write the class name to the tag, such as. The class selector is for a class of tags with the same class name, and there can be multiple class with the same name.

Priority: 10ID selector # div {width:100px; … }

When using the ID selector, we need to write the ID name to the tag, such as. The ID selector will target the tag of this ID name, and only one ID with the same name can exist.

Priority: 100

3. Priority of introduction mode

Inline > internal and external

Who is effective internally or externally?

If the selector priority is the same, whoever will introduce it will take effect. If the selector priority is different, the selector with high priority takes effect.

CSS box model is a kind of thinking model used by CSS technology which is often used in web design.

Imagine a box with four attributes: margin, border, padding and content. Imagine a box with four attributes: margin, border, padding and content. This is shown in the following figure.

Box model

1. Content (content in the box model)

Let's learn the box model through a Demo.

Demo

Through the above code, we can see a red block with the width and height of 100px on the page. As you can see here, the content in the box model can not only set the width and height (except for inline elements), but also add a background. (press F12 in the browser to open the developer tool shown above)

1.1. The use of background

Background-color sets the background color

Attribute values are color values. There are five ways to write them.

English such as red,yellow,blue,cyan... Hexadecimal such as # ffffff... Hexadecimal abbreviations such as # fff... Rgb such as rgb (2557.0255). Rgba such as rgba (255, 255, 255, 255, 0.5).

Background-image sets the background picture

Background-image=url ("picture path")

Background-position sets background positioning

Background-position has two attribute values, the first is generally a horizontal offset and the second is generally a longitudinal offset. If only one value is set, the other value defaults to center.

Property values can be: left, right, top, bottom, center, and pixels.

Backfround-repeat sets the repetition of the background

The default value of repeat spreads the background all over the box model. Repeat-x background is tiled horizontally. The repeat-y background is tiled vertically. No-repeat does not repeat.

Compound Writing method of background

The order of writing is: color, picture, positioning, repetition.

Background-attachment sets whether the background image scrolls with the page

The default value for background-attachment is scroll, that is, the background image scrolls as the page scrolls. You can also fill in fixed, that is, the background image will not scroll with the page, but will cause an offset, generally not used.

Next, modify Demo a little bit and take a look at the example.

Demo.gif

You can see that the background image of the brief book is fixed, and the offset can be observed by commenting out background-attachment: fixed;.

2. Padding (inside margin in the box model)

Or use a chestnut to see what the inside margin is.

Demo

When I move my mouse over the div tab, it shows that the width and height of the div is 300x300.

This is because I set width: 100px for div; height: 100px; so the width and height of div is 100x100, and the middle piece is 100x100.

In addition, I set padding: 100px for div; so the div has the inner margin of 100px in the upper, right, lower and left directions, as shown in the outer circle of the picture, because the inner margin is inside the box, so the inner margin will enlarge our box.

So the width of div is: padding-left + width+ padding-right=100 + 100 + 100. Similarly, the height of div is: padding-top + height + padding-bottom=100 + 100 + 100.

From the formula above, we can see that padding is divided into top, right, bottom and left, and we can also set a different width for each edge. For example, if the upper right, lower left and lower left are 10px 20px 30px 40px respectively, you can write like this.

But it's still too troublesome to write like this, and there's a more concise way to write it.

This method of writing can also achieve the inner margin of the upper right, lower left and 10px 20px 30px 40px, respectively.

Of course, the attribute values of padding can vary from 1 to 4, and the direction controlled by different number of attribute values is shown in the following figure.

The edge corresponding to the padding attribute value

3. Border (the border in the box model)

Add border to div based on the original

Border

You can see that border is also included in the box model, and border will also affect the size of the box model. I use the compound method of border, including the width, style and color of the border. We can also take it apart and write it. The attribute is written as shown in the following figure.

Border

4. Margin (outer margin in the box model)

Margin is similar to padding, but margin is outside the box and is used to control the position between the box and the box. Margin can set negative numbers.

There are two special cases of margin

If two elements are sibling, the margin-bottom of the first element is superimposed with the margin-top of the second element.

Superposition of margin

From a code point of view, the distance between the red block and the blue block should be the margin-bottom of the red block, plus the margin-top of the blue block, but it actually takes the maximum margin value between the boxes. But this is not the case with margin-right and margin-left.

If the two elements are parent-child, the margin-top of the first element in the child is passed to the parent

Then set margin-top: 50px for div_2

The transmission of margin-top. Png

This is obviously not the effect I want, so how can we solve this problem? Let's take a look at the solution.

Set border to parent set padding to parent set overflow: "hidden"

I have already told you the way, and you have to try it for yourself.

Let's take a look at the calculation of the actual size of the box model.

Horizontal: border-left + padding-left + width + padding-right + border-right

Vertical: border-top + padding-top + height + padding-bottom + border-bottom

Five javascript

JavaScript, a literal scripting language, is a dynamically typed, weakly typed, prototype-based language with built-in support for types. Its interpreter, called JavaScript engine, is a part of the browser and is widely used in the client scripting language. It was first used on HTML (an application under the standard general markup language) web pages to add dynamic functions to HTML web pages.

In 1995, it was first designed and implemented by Brendan Eich of Netscape on Netscape Navigator browser. Because Netscape works with Sun, Netscape management wants it to look like Java, so it is named JavaScript. But in fact, its grammar style is similar to that of Self and Scheme. [1]

In order to gain technical advantage, Microsoft launched JScript,CEnvi and ScriptEase, which can run on browsers as well as JavaScript. For uniform specification, JavaScript is also called ECMAScript because it is compatible with the ECMA standard.

ECMAScript, which describes the language

Javascript composition

The grammar and basic object of speech.

Document object Model (DOM), which describes the methods and interfaces for dealing with web page content.

Browser object Model (BOM), which describes the methods and interfaces for interacting with browsers.

JavaScript is a scripting language belonging to the network, which has been widely used in Web application development. It is often used to add a variety of dynamic functions to web pages and provide users with a more smooth and beautiful browsing effect. Usually JavaScript scripts implement their own functions by embedding them in HTML. [3]

Is an interpretive scripting language (the code is not precompiled).

Mainly used to add interactive behavior to HTML (an application under the standard general markup language) page.

You can embed a HTML page directly, but writing it as a separate js file facilitates the separation of structure and behavior.

Cross-platform feature, supported by most browsers, can run on a variety of platforms (such as Windows, Linux, Mac, Android, iOS, etc.).

Like other languages, Javascript scripting language has its own basic data types, expressions and arithmetic operators, and a basic programming framework for programs. Javascript provides four basic data types and two special data types for processing data and text. While variables provide a place to store information, expressions can complete more complex information processing. [5]

Embed dynamic text in the HTML page.

Respond to browser events.

Read and write HTML elements.

Validate the data before it is submitted to the server.

Detect the browser information of the visitor.

Control cookies, including creation and modification, etc.

Server-side programming based on Node.js technology.

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