Code Style
File
[MUST] JavaScript Source files must be encoded in UTF-8 without BOM.
Indentation
[MUST] 4 space indentation. tabs and 2 space are not allowed.
[MUST] case and default in switch must be indented.
// good
switch (variable) {
case '1':
// do...
break;
case '2':
// do...
break;
default:
// do...
}
// bad
switch (variable) {
case '1':
// do...
break;
case '2':
// do...
break;
default:
// do...
}
Space
[MUST] Set off binary operator with spaces. But place no space between unary operator and its operand.
let a = !arr.length;
a++;
a = b + c;
[MUST] Place 1 space before the leading brace.
// good
if (condition) {
}
set('attr', {
some: 'xxx',
any: 'yyy'
});
function funcName() {
}
// bad
if (condition){
}
set('attr',{
some: 'xxx',
any: 'yyy'
});
function funcName(){
}
[MUST] Place 1 space after if / else / for / while / function / switch / do / try / catch / finally.
// good
if (condition) {
}
while (condition) {
}
(function () {
})();
// bad
if(condition) {
}
while(condition) {
}
(function() {
})();
[MUST] In the object creating statement, place 1 space after :, but no space before it.
// good
const obj = {
a: 1,
b: 2,
c: 3
};
// bad
const obj = {
a : 1,
b:2,
c :3
};
[MUST] Place no space between the function name and ( in function declaration, expression of named function and function call.
// good
function funcName() {
}
const funcName = function funcName() {
};
funcName();
// bad
function funcName () {
}
const funcName = function funcName () {
};
funcName ();
[MUST] Place no space between , and ;.
// good
callFunc(a, b);
// bad
callFunc(a , b) ;
[MUST] Place no space after ( and [ and before ) and ].
// good
callFunc(param1, param2, param3);
save(this.list[this.indexes[i]]);
needIncream && (variable += increament);
if (num > list.length) {
}
while (len--) {
}
// bad
callFunc( param1, param2, param3 );
save( this.list[ this.indexes[ i ] ] );
needIncreament && ( variable += increament );
if ( num > list.length ) {
}
while ( len-- ) {
}
// good
const arr1 = [];
const arr2 = [1, 2, 3];
const obj1 = {};
const obj2 = {name: 'obj'};
const obj3 = {
name: 'obj',
age: 20,
sex: 1
};
// bad
const arr1 = [ ];
const arr2 = [ 1, 2, 3 ];
const obj1 = { };
const obj2 = { name: 'obj' };
const obj3 = {name: 'obj', age: 20, sex: 1};
[MUST] Must no trailing space in each line.
Line Break
[MUST] Place line break in the end of a statement.
[MUST] No more than 120 characters per line.
[MUST] Place operator at the beginning of a line if it break lines.
// good
if (user.isAuthenticated()
&& user.isInRole('admin')
&& user.hasAuthority('add-admin')
|| user.hasAuthority('delete-admin')
) {
// Code
}
const result = number1 + number2 + number3
+ number4 + number5;
// bad
if (user.isAuthenticated() &&
user.isInRole('admin') &&
user.hasAuthority('add-admin') ||
user.hasAuthority('delete-admin')) {
// Code
}
const result = number1 + number2 + number3 +
number4 + number5;
[MUST] Start a new line for ), ], } if the content inside the brackets occupies multiple lines.
Make the same indent as the line where the corresponding (, [, { placed.
// good
if (product) {
product.load();
if (user.isAuthenticated()
&& user.isInRole('admin')
&& user.hasAuthority('add-admin')
) {
sendProduct(user, product);
}
}
const arr = [
'candy', 'sugar'
];
// bad
if (product) {
product.load();
if (user.isAuthenticated()
&& user.isInRole('admin')
&& user.hasAuthority('add-admin')) {
sendProduct(user, product);
}
}
const arr = [
'candy', 'sugar'
];
[MUST] Must not break lines before , or ;.
// good
const obj = {
a: 1,
b: 2,
c: 3
};
foo(
aVeryVeryLongArgument,
anotherVeryLongArgument,
callback
);
// bad
const obj = {
a: 1
, b: 2
, c: 3
};
foo(
aVeryVeryLongArgument
, anotherVeryLongArgument
, callback
);
[SUGGEST] Suggestion about line break and indent:
if (user.isAuthenticated()
&& user.isInRole('admin')
&& user.hasAuthority('add-admin')
) {
// Code
}
foo(
aVeryVeryLongArgument,
anotherVeryLongArgument,
callback
);
baidu.format(
dateFormatTemplate,
year, month, date, hour, minute, second
);
$('#items')
.find('.selected')
.highlight()
.end();
const result = thisIsAVeryVeryLongCondition
? resultA : resultB;
const res = condition
? thisIsAVeryVeryLongResult
: resultB;
[MUST] Start a new line for else and catch if using multi-line blocks.
// good
if (condition) {
// some statements;
}
else {
// some statements;
}
try {
// some statements;
}
catch (ex) {
// some statements;
}
// bad
if (condition) {
// some statements;
} else {
// some statements;
}
try {
// some statements;
} catch (ex) {
// some statements;
}
Statement
[MUST] The semicolon must not be ignored at the end of a statement.
[MUST] The {} must not be ignored even if there is only one line.
// good
if (condition) {
callFunc();
}
// bad
if (condition) callFunc();
if (condition)
callFunc();
[MUST] Place no semicolon at the end of a function definition.
// good
function funcName() {
}
// bad
function funcName() {
};
// For function expression, the semicolon must not be ignored.
const funcName = function () {
};
[MUST] No trailing comma in object and array declarations.
// good
const obj = {
attr1: 'xxx',
attr2: 'yyy'
};
const arr = [
'xxx',
'yyy'
];
// bad
const obj = {
attr1: 'xxx',
attr2: 'yyy',
};
const arr = [
'xxx',
'yyy',
];
Naming Conventions
[MUST] Use lowerCamelCase for variables, properties and function names.
const loadingModules = {};
function loadProduct() {
}
[MUST] Use UpperCamelCase (Pascal) for class names.
function Element(options) {
}
[SUGGEST] All of the letters of a abbreviation should be both upper cases or both lower cases.
function parseSVG() {
}
const svgParser;
Language features
Compatibility
Language features can be polyfilled by some utilities, but must not by modifying the prototype of the built-in JS objects.
// good
import * as zrUtil from 'zrender/src/core/util';
zrUtil.each(array, function (val, index) {
sum += val;
});
const result = zrUtil.map(array, function (val) {
return parse(val);
});
const pos = zrUtil.indexOf(array, val);
const obj2 = zrUtil.extend({}, obj1);
function Element() {
// ...
}
// bad
array.forEach(function (val, index) {
sum += val;
});
let result = array.map(function (val) {
return parse(val);
});
const pos = array.indexOf(val);
const obj2 = Object.assign({}, obj1);
class Element {
// ...
}
String.prototype.trim = function () {
};
Variable
[MUST] Prefer using const to declare variable. And one line can not declares more than one variable.
// good
const name = 'MyName';
const hangModules = [];
const missModules = [];
const visited = {};
// bad
name = 'MyName';
const hangModules = [],
missModules = [],
visited = {};
Condition
[MUST] In equality expression, == can only be used on null or undefined detection. === should be used in the rest of cases .
// good
if (age === 30) {
// ...
}
if (type == null) {
// ...
}
// bad
if (age == 30) {
// ......
}
[SUGGEST] Use xxx == null to determine null or undefined.
[SUGGEST] Try best to make the meaning of null and undefined the same, namely, do not make users or developers distinguishing whether a variable is null or undefined.
[SUGGEST] The function expression or function declaration should not be placed inside a loop body.
// good
function clicker() {
// ......
}
for (let i = 0, len = elements.length; i < len; i++) {
const element = elements[i];
addListener(element, 'click', clicker);
}
// bad
for (let i = 0, len = elements.length; i < len; i++) {
const element = elements[i];
addListener(element, 'click', function () {});
}
Type Conversion
[SUGGEST] Use + '' to convert a value to string.
// good
num + '';
// bad
new String(num);
num.toString();
String(num);
[SUGGEST] Use + to convert a value to number.
// good
+str;
// bad
Number(str);
[MUST] The second parameter must not be ignored when using parseInt.
// good
parseInt(str, 10);
// bad
parseInt(str);
String, Object, Array
[MUST] Use ' but not " to define a string.
[MUST] Use object literal {} to create a plain object.
// good
const obj = {};
// bad
const obj = new Object();
[MUST] If all of the properties of an object literal do not need quotation marks, they should ignore them. If quotation marks is necessary, use ' but not ".
// good
const info = {
name: 'someone',
age: 28
};
// bad
const info = {
'name': 'someone',
'age': 28
};
const info2 = {
"age": 40
};
[MUST] The prototype of built-in objects must not be modified.
// Forbidden
String.prototype.trim = function () {
};
[SUGGEST] Try best to use . but not [] to visit properties of an object.
[SUGGEST] hasOwnProperty should be used to when using for ... in ..., in case that some extra properties is added on the prototype of Object in some runtime environment.
const newInfo = {};
for (const key in info) {
if (info.hasOwnProperty(key)) {
newInfo[key] = info[key];
}
}
[MUST] Use array literal [] to create an array, except intending to create an array with a given length.
// good
const arr = [];
const arr2 = new Array(1e4);
// bad
const arr = new Array();
[MUST] Do not use for in in array traverse.
Others
[MUST] Do not use eval and with. new Function can be used.