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This time I will bring you what JS code specifications released by Google, and what are the precautions when using the JS code specifications released by Google. The following is a practical case, let’s take a look. . Google has released a JS code specification for those who are not familiar with coding specifications. It lists best practices for writing concise and understandable code.
Code specification is not a rule for writing correct
JavaScriptcode, but a choice to maintain a consistent source code writing pattern. This is especially true for the JavaScript language, as it is flexible and less restrictive, allowing developers to use many different coding styles. Google and Airbnb each occupy half of the most popular coding standards. If you will invest a long time in writing JS code, I strongly recommend that you read through the coding standards of these two companies.
What I want to write next are the thirteen rules that I personally think are closely related to daily development in Google's code specifications.
The issues they deal with are very controversial, including tabs and spaces, whether to force the use of semicolons, etc. There are also some rules that surprise me and often end up changing my habits of writing JS code.
For each rule, I will first give a summary of the specification and then quote the detailed description from the specification. I will also give some appropriate counterexamples to demonstrate the importance of following these rules.
The specification then states that indentation should be achieved using 2 spaces instead of 4.
// bad
function foo() {
∙∙∙∙let name;
}
// bad
function bar() {
∙let name;
}
// good
function baz() {
∙∙let name;
}
Although I don't understand why anyone would object to this rule, the use of semicolons has apparently become as controversial as the "spaces vs tabs" issue. Google said that the semicolon is necessary and cannot be omitted.
// bad
let luke = {}
let leia = {}
[luke, leia].forEach(jedi => jedi.father = 'vader')
// good
let luke = {};
let leia = {};
[luke, leia].forEach((jedi) => {
jedi.father = 'vader';
});
// 暂时不要编写下面的代码：
//------ lib.js ------
export function square(x) {
return x * x;
}
export function diag(x, y) {
return sqrt(square(x) + square(y));
}
//------ main.js ------
import { square, diag } from 'lib';
Translator's Note: I feel that it is unrealistic to comply with this norm. After all, babel already exists. And when using React, the best practice is to use ES6 modules.
Aligning the code horizontally will add some extra spaces in the code, which makes the characters on two adjacent lines appear to be on a vertical line.
// bad
{
tiny: 42,
longer: 435,
};
// good
{
tiny: 42,
longer: 435,
};
I don’t know if it’s because no one can convince them, or if it’s because old habits die hard. Currently I still see many people using var to declare variables on StackOverFlow or elsewhere.
// bad var example = 42; // good const example = 42;
// bad
[1, 2, 3].map(function (x) {
const y = x + 1;
return x * y;
});
// good
[1, 2, 3].map((x) => {
const y = x + 1;
return x * y;
});
在处理多行字符串时，模板字符串比复杂的拼接字符串要表现的更出色。
// bad
function sayHi(name) {
return 'How are you, ' + name + '?';
}
// bad
function sayHi(name) {
return ['How are you, ', name, '?'].join();
}
// bad
function sayHi(name) {
return `How are you, ${ name }?`;
}
// good
function sayHi(name) {
return `How are you, ${name}?`;
}
在JS中，\也代表着续行符。Google的代码规范不允许在不管是模板字符串还是普通字符串中使用续行符。尽管ES5中允许这么做，但如果在\后跟着某些结束空白符，这种行为会导致一些错误，而这些错误在审阅代码时很难注意到。
这条规则很有趣，因为Airbnb的规范中有一条与之不相同的规则
Google推荐下面这样的写法，而Airbnb则认为应该顺其自然，不做特殊处理，该多长就多长。
// bad (建议在PC端阅读) const longString = 'This is a very long string that \ far exceeds the 80 column limit. It unfortunately \ contains long stretches of spaces due to how the \ continued lines are indented.'; // good const longString = 'This is a very long string that ' + 'far exceeds the 80 column limit. It does not contain ' + 'long stretches of spaces since the concatenated ' + 'strings are cleaner.';
在ES6中，有3种不同的for循环。尽管每一种有它的应用场景，但Google仍推荐使用for...of。
真有趣，Google居然会特别指定一种for循环。虽然这很奇怪，但不影响我接受这一观点。
以前我认为for...in适合遍历Object，而for...of适合遍历数组。因为我喜欢这种各司其职的使用方式。
尽管Google的规范与这种使用方式相冲突，但Google对for...of的偏爱依然让我觉得十分有趣。
除非是在code loader中，否则不用使用eval或是Function(...string)结构。这个功能具有潜在的危险性，并且在CSP环境中无法起作用。
MDN中有一节专门提到不要使用eval语句。
// bad
let obj = { a: 20, b: 30 };
let propName = getPropName(); // returns "a" or "b"
eval( 'var result = obj.' + propName );
// good
let obj = { a: 20, b: 30 };
let propName = getPropName(); // returns "a" or "b"
let result = obj[ propName ]; // obj[ "a" ] is the same as obj.a
常量命名应该使用全大写格式，并用下划线分割
如果你确定一定以及肯定一个变量值以后不会被修改，你可以将它的名称使用全大写模式改写，暗示这是一个常量，请不要修改它的值。
遵守这条规则时需要注意的一点是，如果这个常量是一个函数，那么应该使用驼峰式命名法。
// bad const number = 5; // good const NUMBER = 5;
每一个变量声明都应该只对应着一个变量。不应该出现像let a = 1,b = 2;这样的语句。
// bad let a = 1, b = 2, c = 3; // good let a = 1; let b = 2; let c = 3;
只允许使用单引号包裹普通字符串，禁止使用双引号。如果字符串中包含单引号字符，应该使用模板字符串。
// bad let directive = "No identification of self or mission." // bad let saying = 'Say it ain\u0027t so.'; // good let directive = 'No identification of self or mission.'; // good let saying = `Say it ain't so`;
就像我在开头所说那样，规范中没有需要强制执行的命令。尽管Google是科技巨头之一，但这份代码规范也仅仅是用来当作参考罢了。
Google是一家人才汇聚的科技公司，雇佣着出色的程序员来编写优秀的代码。能够看到这样的公司发布的代码规范是一件很有趣的事情。
如果你想要实现一种Google式的代码，那么你可以在项目中制定这些规范。但你可能并不赞成这份代码规范，这时也没有人会阻拦你舍弃其中某些规则。
我个人认为在某些场景下，Airbnb的代码规范比Google的代码规范要出色。但不管你支持哪一种，也不管你编写的是什么类型的代码，最重要的是在脑海中时刻遵守着同一份代码规范。
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