You definitely need the front-end code specification

In daily work, if we want to write high quality code, write beautiful, it must need a set of code specifications, the following code specifications are from Jingdong Cave laboratory, here also want to keep notes for daily review.

CSS code specification

Code style.

There are two styles of style writing, Compact

.jdc{ dispaly: block; width: 50px; }Copy the code

One is called Expanded

.jdc {
    dispaly: block;
    width: 50px;
}
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Uniform convention expansion format writing in the team

Code case

The style selector, attribute name, and attribute value keywords are all written in lower case, and the attribute string is case-sensitive.

Recommend * / / *
.jdc {
    display: block;
}
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/* not recommended */
.JDC {
    DISPLAY: BLOCK;
}
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The selector

* Do not use ID selectors. Do not use tag selectors without specific semantic definitions

Recommend * / / *
.jdc {}
.jdc li {}
.jdc li p {}
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/* not recommended */* {}#jdc {}
.jdc div{}
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Code indentation

Use four Spaces to indent code so that all editors behave the same (each editor has its own configuration)

.jdc {
    width: 100%;
    height: 100%;
}
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A semicolon

Each attribute declaration ends with a semicolon;

.jdc {
    width: 100%;
    height: 100%;
}
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Code legibility

A space between the open parenthesis and the class name, and a space between the colon and the attribute

Recommendation:

.jdc {
    width: 100%;
}
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Is not recommended:

.jdc{
    width:100%;
}
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Comma-separated values, followed by a space

Recommendation:

.jdc {
    box-shadow: 1px 1px 1px # 333.2px 2px 2px #ccc;
}
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Is not recommended:

.jdc {
    box-shadow: 1px 1px 1px # 333.2px 2px 2px #ccc;
}
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Opens a new line for a single CSS selector or new declaration

Recommendation:

.jdc..jdc_logo..jdc_hd {
    color: #ff0;
}
.nav {
    color: #fff;
}
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Is not recommended:

.jdc..jdc..jdc_hd{
    color: #ff0;
}.nav{
    color: #fff;
}
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Color Value RGB () RGBA () HSL () HSLA () Rect () does not contain Spaces, and the value does not contain an unnecessary 0

Recommendation:

.jdc {
    color: rgba(255.255.255.5);
}
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Is not recommended:

.jdc {
    color: rgba( 255.255.255.5);
}
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Property value Hexadecimal value can be abbreviated if possible

Recommendation:

.jdc {
    color: #fff;
}
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Is not recommended:

.jdc {
    color: #ffffff;
}
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Do not specify unit recommendations for 0:

.jdc {
    margin: 0 10px;
}
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Is not recommended:

.jdc {
    margin: 0px 10px;
}
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attribute

Attribute value quotes

Single quotation marks are used for CSS attribute values

Recommend * / / *
.jdc {
    font-family: 'Hiragino Sans GB';
}
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/* not recommended */
.jdc {
    font-family: "Hiragino Sans GB";
}
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Attribute writing order

The following order is recommended:

Display/position/float/clear/visibility/overflow display/position/float/clear/visibility/overflow Width/height/margin/padding/border/background Color/font/text-decoration/text-align/vertical-align/white-space/break-word content / cursor / border-radius / box-shadow /text-shadow / background:linear-gradient

.jdc {
    display: block;
    position: relative;
    float: left;
    width: 100px;
    height: 100px;
    margin: 0 10px;
    padding: 20px 0;
    font-family: Arial, 'Helvetica Neue', Helvetica, sans-serif;
    color: # 333;
    background: rgba(0.0.0.5);
    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    -o-border-radius: 10px;
    -ms-border-radius: 10px;
    border-radius: 10px;
}
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CSS3 private prefix

The CSS3 browser private prefix precedes the standard prefix

.jdc {
    -webkit-border-radius: 10px;
    -moz-border-radius: 10px;
    -o-border-radius: 10px;
    -ms-border-radius: 10px;
    border-radius: 10px;
}
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JS code specification

Language specification

JavaScript is a client-side scripting language, and here are the rules you need to follow when writing JavaScript.

reference

Const and let are both block-level scopes, and var is function-level scopes

    Const and let only exist in the blocks they define
    {
        let a = 1
        const b = 1
    }
    console.log(a)  // ReferenceError
    console.log(b)  // ReferenceError
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Use const for all references and do not use var

Reason: This ensures that you can’t reassign references to avoid errors and unintelligible code

    // bad
    var a = 1
    var b = 2

    // good
    const a = 1
    const b = 2
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If the reference is mutable, use let instead of var

Reason: Let is block-scoped, unlike VAR, which is function-scoped

// bad
    var count = 1
    if (count < 10) {
        conut += 1
    }

    // good
    let count = 1
    if (count < 10) (
        count += 1
    )
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object

Create objects using literal values

    // bad
    const a = new Object{}

    // good
    const a = {}
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Do not use reserved words as keys for objects, as this will not run under IE8

    // bad
    const a = {
        default: {},  // Default is reserved
        common: {}}// good
    const a = {
        defaults: {},
        common: {}}Copy the code

When you create an object with a dynamic property name, use the object calculation property name to create the object

Reason: Because doing so allows you to define all object properties in one place

    function getKey(k) {
        return `a key named ${k}`
    }

    // bad
    const obj = {
        id: 5.name: 'San Francisco'
    };
    objp[getKey('enabled')] = true

    // good
    const obj = {
        id: 5.name: 'San Francisco',
        [getKey('enabled')]: true
    }
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Use the shorthand for object methods

    // bad
    const item = {
        value: 1.addValue: function (val) {
            return item.value + val
        }
    }

    // good
    const item = {
        value: 1,
        addValue (val) {
            return item.value + val
        }
    }
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Use the shorthand for the value of an object property

Reason: It’s shorter and clearer

    const job = 'FrontEnd'

    // bad
    const item = {
        job: job
    }

    // good
    const item = {
        job
    }
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Group abbreviated object attributes at the beginning of the object declaration

Reason: This makes it easier to tell which attributes are abbreviated

    const job = 'FrontEnd'
    const department = 'JDC'

    // bad
    const item = {
        sex: 'male',
        job,
        age: 25,
        department
    }

    // good
    const item = {
        job,
        department,
        sex: 'male'.age: 25
    }
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Use quotation marks only for attributes with invalid identifiers

Reason: Because in general we think it’s subjectively easier to read, which leads to improved code highlighting and optimizations by major JS engines

    // bad
    const bad = {
        'foo': 3.'bar': 4.'data-blah': 5
    }

    // good
    const good = {
        foo: 3.bar: 4.'data-blah': 5
    }
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Don’t directly use object. prototype methods such as hasOwnProperty, propertyIsEnumberable and isPrototypeOf

Cause: These methods may be overridden by the Object’s own property of the same name – such as {hasOwnProperty: false} or the Object may be a null Object (object.create (null)).

    // bad
    console.log(object.hasOwnProperty(key))

    // good
    console.log(object.prototype.hasOwnProperty.call(object, key))

    // best
    const has = Object.prototype.hasOwnProperty  // cache the lookup once, in module scope.
    console.log(has.call(object, key)
    )
    /* or */
    import has from 'has' // https://www.npmjs.com/package/has
    console.log(has(object, key))
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Preference for object expansion operators… To make a shallow copy of the Object instead of using Object.assgin, use the Object residual operator to get a new Object containing the identified residual attributes

    // very bad
    const original = { a: 1.b: 2 }
    const copy = Object.assgin(original, { c: 3 })  // Changes the original array

    // bad 
    const original = { a: 1.b: 2 }
    const copy = Object.assgin({}, original, { c: 3 })  // copy => { a: 1, b: 2, c: 3}

    // good
    const original = { a: 1.b: 2 }
    constcopy = { ... original,c: 3}  // copy => { a: 1, b: 2, c: 3 }

    const{ a, ... noA } = copy// noA => { b: 2, c: 3 }

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An array of

Create an array using literal values

    // bad
    const items = new Array(a)// good
    const item = []
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When adding elements to an array, use the push method

    const items = []
    
    // bad
    items[items.length] = 'test'

    // good
    items.push('test')
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Using the expansion operator… Copy the array

    // bad
    const items = []
    const itemsCopy = []
    const len = items.length
    let i

    // bad
    for (i = 0; i < len; i++) {
        itemsCopy[i] = items[i]
    }

    // good
    itemsCopy = [...items]
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To convert an iterable object into an array, use the expansion operator… Instead of an Array. The from

    const foo = document.querySelectorAll('.foo')

    // good 
    const nodes = Array.from(foo)

    // best
    const nodes = [...foo]
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Convert an array-like object to an Array using array. from

    const arrLike = { 0: 'foo'.1: 'bar'.2: 'baz'.length: 3}

    // bad
    const arr = Array.prototype.slice.call(arrLike)

    // good
    const arr = Array.from(arrLike)
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Use array. from instead of the extension operator when iterating over the mapping… Because it avoids creating intermediate arrays

    // bad
    const baz = [...foo].map(bar)

    // good
    const baz = Array.from(foo, bar)
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When using a method such as an array map, use a return declaration. In the case of a single declaration statement, omit the return declaration

    // good
    [1.2.3].map(x= > {
        const y = x + 1
        return x * y
    })

    // good
    [1.2.3].map(x= > x + 1)

    // bad
    const flat = {}
    [[0.1], [2.3], [4.5]].reduce((memo, item, index) = > {
        const flatren = memo.concat(item)
        flat[index] = flatren
    })

    // good
    const flat = {}
    [[0.1], [2.3], [4.5]].reduce((memo, item, index) = > {
        const flatren = memo.concat(item)
        flat[index] = flatren
        return flatten
    })

    // bad
    inbox.filter((msg) = > {
        const { subject, author } = msg
        if (subject === 'Mockingbird') {
            return author === 'Harper Lee'
        } else {
            return false}})// good
    inbox.filter((msg) = > {
        const { subject, author } = msg
        if (subject === 'Mockingbird') {
            return author === 'Harper Lee'
        }

        return false
    })
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If an array has more than one line, use the new line after the opening parentheses and before the closing parentheses

    // bad
    const arr = [
        [0.1], [2.3], [4.5]]const objectInArray = [{
        id: 1
    }, {
        id: 2
    }]

    const numberInArray = [
        1.2
    ]

    // good
    const arr = [[0.1], [2.3], [4.5]]
    
    const objectInArray = [
        {
            id: 1
        },
        {
            id: 2}]const numberInArray = [
        1.2
    ]
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Structure assignment

Use structural assignment when you need to use multiple attributes of an object

Level 2 nesting wishes: Structures avoid creating temporary references to attributes

    // bad
    function getFullName (user) {
        const firstName = user.firstName
        const lastName = user.lastName
        
        return `${firstName} ${lastName}`
    }
    
    // good 
    function getFullName (user) {
        const { firstName, lastName } = user
        
        return `${firstName} ${lastName}`
    }

    // better
    function getFullName ({ firstName, lastName }) {
        return `${firstName} ${lastName}`
    }
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When you need to use multiple values of an array, use structural assignment as well

    const arr = [1.2.3.4]

    // bad
    const first = arr[0]
    const second = arr[1]

    // good
    const [first, second] = arr
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When a function needs to return multiple values, use the structure of an object, not an array

Reason: Attribute order can be added or changed at any time, nondestructively

    // bad
    function doSomething () {
        return [top, right, bottom, left]
    }

    // If it is an array structure, then the order of the data needs to be considered when calling
    const [top, xx, xxx, left] = doSomething

    // good
    function doSomething () {
        return {top, right, bottom, left}
    }

    // There is no need to consider the order of the data
    const { top, left } = doSomething
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string

Use single quotation marks for strings.

    // bad
    const department = "JDC"

    // good
    const department = 'jdc'
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When the string is too long, do not use the string concatenator \, but use + instead

    const str = 'Bump Lab bump Lab Bump Lab bump Lab' + 
        'Bump Lab bump Lab Bump Lab bump Lab' + 
        'Bump Lab bump Lab'
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When programmatically generating strings, use template strings

    const test = 'test'

    // bad
    cosnt str = ['a'.'b', test].join()

    // bad
    const str = 'a' + 'b' + test

    // good
    const str = `ab${test}`
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Do not use eval() on strings; it leads to too many bugs
Do not use unnecessary escape characters in strings

    // bad
    const foo = '\'this\' \i\s \"quoted\"'

    // good
    const foo = '\'this\' is "quoted"'
    const foo = `my name is '${name}'`
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function

Do not use the Function constructor to create functions

Reason: Creating functions this way creates vulnerabilities just like using eval() on strings

    // bad
    const add = new Function('a'.'b'.'return a + b')

    // still bad
    const subtract = Function('a'.'b'.'return a + b')
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Use Spaces in function signatures

    // bad
    const f = function(){}
    const g = function (){}
    const c = function() {}

    // good
    const x = function b () {}
    const y = function c () {}
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Use named function expressions instead of function declarations

The reason for doing so is that function declarations are elevated, which means that it is easy to refer to the function before it is defined in the file, which is bad for readability and maintainability. If you find that the function definition is too large and complex to understand the rest of the file, maybe you should break it up into modules! Don’t forget to name the expression explicitly, regardless of whether the name is inferred from the included variable (often found in modern browsers or when using the Babel compiler). This eliminates any assumptions in the error call stack. (the discussion)

    // bad
    function foo () {
        // ...
    }

    // bad
    const foo = function () {
        // ...
    }

    // good
    // lexical name distinguished from the variable-referenced invocation(s)
    const short = function longUniqueMoreDescriptiveLexicalFoo () {
        // ...
    }
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Wrap self-executing anonymous functions in parentheses

Why: An immediately executed anonymous function expression is a single unit, and wrapping it and its call parentheses in parentheses makes this clear. Note that IIFE is hardly needed in a world full of modules.

    // immediately-invoked function expression (IIFE)
    (function () {
    console.log('Welcome to the Internet. Please follow me.')
    }())
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Do not declare functions in non-functional blocks of code (if, while, etc.)

    // bad
    if (isUse) {
        function test () {
            // do something}}// good
    let test
    if (isUse) {
        test = () = > {
            // do something}}Copy the code

Do not name arguments as arguments will take precedence over arguments objects that previously existed in each function scope

    // bad
    function foo (name, options, arguments) {
        // ...
    }

    // good
    function foo (name, options, args) {
        // ...
    }
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Instead of arguments, use residual operators…

Arguments is just an array of classes, and… It’s a real array

    // bad
    function test () {
        const args = Array.prototype.slice.call(arguments)
        return args.join(' ')}// good
    function test (. args) {
        return args.join(' ')}Copy the code

You definitely need the front-end code specification

CSS code specification

Code style.

Code case

The selector

Code indentation

A semicolon

Code legibility

Attribute value quotes

Attribute writing order

CSS3 private prefix

JS code specification

Language specification

reference

object

An array of

Structure assignment

string

function

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