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NativeScript Modules Coding Convention

Linting

We use TSLint for linting. Rules are defined in build/tslint.json. Run the tslint from the root of the repo with:

npm run tslint

Tabs vs Spaces

Use 4 spaces indentation.

Line length

Try to limit your lines to 80 characters.

Semicolons, statement Termination

Always use semicolons where it is appropriate.

Right:

let x = 1;

Wrong:

let x = 1

Quotes

Use double quotes for strings:

Right:

let foo = "bar";

Wrong:

let foo = 'bar';

Braces

Your opening braces go on the same line as the statement.

Right:

if (true) {
    console.log("winning");
}

Wrong:

if (true)
{
    console.log("losing");
}

Also, notice the use of whitespace before and after the condition statement.

Follow the JavaScript convention of stacking else/catch clauses on the same line as the previous closing brace.

Right:

if (i % 2 === 0) {
    console.log("even");
} else {
    console.log("odd");
}

Wrong:

if (i % 2 === 0) {
    console.log("even");
}
else {
    console.log("odd");
}

Variable declarations

Declare variables with let instead of var. Use const when possible.

Right:

const button = new Button();

for (let i = 0; i < items.length; i++) {
    // do something
}

Wrong:

var button = new Button();

for (var i = 0; i < items.length; i++) {
    // do something
}

Variable and property names

Variables and properties should use lower camel case capitalization. They should also be descriptive. Single character variables and uncommon abbreviations should generally be avoided unless it is something well known as i in for loops

Right:

let adminUser = db.query("SELECT * FROM users ...");

Wrong:

let admin_user = db.query("SELECT * FROM users ...");

Type names

Type names should be capitalized using upper camel case.

Right:

class UserAccount() {
  this.field = "a";
}

Wrong:

class userAccount() {
  this.field = "a";
}

Constants

Constants should be declared with CAPITAL letters and const keyword. Use underscore to name constants with complex wording.

Right:

const SECOND = 1 * 1000;
const MY_SECOND = SECOND;

Wrong:

var second = 1 * 1000;

Object / Array creation

Use trailing commas and put short declarations on a single line. Only quote keys when your interpreter complains:

Right:

let a = ["hello", "world"];
let b = {
  good: "code",
  "is generally": "pretty",
};

Wrong:

let a = [
  "hello", "world"
];
let b = {"good": "code"
        , is generally: "pretty"
        };

Equality operator

Use the strict comparison operators. The triple equality operator helps to maintain data type integrity throughout code.

Right:

let a = 0;
if (a === "") {
    console.log("winning");
}

Wrong:

let a = 0;
if (a == "") {
    console.log("losing");
}

Short-hand operators

Try to avoid short-hand operators except in very simple scenarios.

Right:

let default = x || 50;
let extraLarge = "xxl";
let small = "s"
let big = (x > 10) ? extraLarge : small;

Wrong:

let default = checkX(x) || getDefaultSize();
let big = (x > 10) ? checkX(x) ? getExtraLarge() : getDefaultSize() : getSmallValue();

Curly braces

Always use curly braces even in the cases of one line conditional operations.

Right:

if (a) {
    return "winning";
}

Wrong:

if (a)
    return "winning";

if (a) return "winning";

Boolean comparisons

Do not directly compare with true or false.

Right:

if(condition) {
    console.log("winning");
}

if (!condition) {
    console.log("winning");
}

Wrong:

if(condition === true) {
    console.log("losing");
}

if(condition !== true) {
    console.log("losing");
}

if(condition !== false) {
    console.log("losing");
}

Boolean conditions format

Do not use the Yoda Conditions when writing boolean expressions:

Right:

let num;
if(num >= 0) {
    console.log("winning");
}

Wrong:

let num;
if(0 <= num) {
    console.log("losing");
}

NOTE It is OK to use constants on the left when comparing for a range.

if(0 <= num && num <= 100) {
    console.log("winning");
}

Function length

Keep your functions short. A good function fits on a slide that the people in the last row of a big room can comfortably read. So don't count on them having perfect vision and limit yourself to 1/2 of your screen height per function (no screen rotation :).

Return statements

There are few important considerations here:

  • To avoid deep nesting of if-statements, always return a functions value as early as possible. In certain routines, once you know the answer, you want to return it to the calling routine immediately. If the routine is defined in such a way that it doesn't require any cleanup, not returning immediately means that you have to write more code.
  • Minimize the number of returns in each routine. It's harder to understand a routine if, reading it at the bottom, you're unaware of the possibility that it returned somewhere above.

Right:

function getSomething(val) {
    if (val < 0) {
        return false;
    }

    if (val > 100) {
        return false;
    }

    let res1 = doOne();
    let res2 = doTwo();
    let options = {
        a: 1,
        b: 2
    };
    let result = doThree(res1, res2, options);
    return result;
}

Wrong:

function getSomething(val) {
    if (val >= 0) {
        if (val < 100) {
            let res1 = doOne();
            let res2 = doTwo();
            let options = {
                             a: 1,
                             b: 2
                          };
            let result = doThree(res1, res2, options);
            return result;    
        }
        else {
            return false;
        }
    }
    else {
        return false;
    }
}

Arrow Functions

Use arrow functions over anonymous function expressions. Typescript will take care for this.

Right:

req.on("end", () => {
    exp1();
    exp2();
    this.doSomething();
});

Wrong:

let that = this;
req.on("end", function () {
    exp1();
    exp2();
    that.doSomething();
});

Comments

Use the JSDoc convention for comments. When writing a comment always think how understandable will be for somebody who is new to this code. Even if it may look simple to you think how a guy that just joined will understand it. Always comment in the following cases:

  • When there is some non-trivial logic.
  • Some "external" knowledge is needed which is missing in the context - workaround for driver, module bug, special 'hack' because of a bug and so on;
  • When you are creating a new class
  • Public methods - include all the arguments and if possible the types {String}, {Number}. Optional arguments should be marked too. Check the @param tag

File/module structure

Typical module should have the following structure:

  1. required dependencies
  2. module-private declarations - variables, functions, classes, etc.
  3. export variables and functions
  4. export class declarations

For more information see this file

File naming

Use lower case for file names. Use dash to separate different words.

Right: file-system

Wrong: FileSystem, fileSystem, file_system

This, that, self

When you need to keep reference to this use that as the name of the variable. Additionally, if you use the TypeScript lambda support, the compiler will take care of this automatically.

Right:

let that = this;
doSomething(function(){
    that.doNothing();
});

Wrong:

let me = this;
doSomething(function(){
    me.doNothing();
});

Private (hidden) variables and methods

Although there is the private keyword in TypeScript, it is only a syntax sugar. There is no such notation in JavaScript and everything is available to the users. Hence, always use underscore (_) to prefix private variables and methods. There are also methods which have the public visibility but they are meant to be used within our code ONLY. Such methods should also be prefixed with underscore.

Right:

class Foo {
    private _myBoolean: boolean;
    
    public publicAPIMethod() {
    }
    
    public _frameworkMethod() {
        // this method is for internal use only
    }
    
    private _doSomething() {
    }
}

Wrong:

class Foo {
    private myBoolean: boolean;
    
    public _publicAPIMethod() {
    }
    
    public frameworkMethod() {
        // this method is for internal use only
    }
    
    private doSomething() {
    }
}

TypeScript optional parameters

Do not use optional parameters in IMPLEMENTATION files. This is because the TS compiler generates additional array and populates its from the arguments object. Still, it is OK to use these in a definition file (as declarations ONLY).

Right:

// declaration
export declare function concat(...categories: string[]): string;

// implementation
export function concat(): string {
    let i;
    let result: string;
    // use the arguments object to iterate the parameters
    for (i = 0; i < arguments.length; i++) {
        // do something
    }

    return result;
}

Wrong:

// declaration
export declare function concat(...categories: string[]): string;

// implementation
export function concat(...categories: string[]): string {
    let i;
    let result: string;
    // use the arguments object to iterate the parameters
    for (i = 0; i < categories.length; i++) {
        // do something
    }

    return result;
}

Naming test functions

Name your test function with test_ so that our test runner can find them and add 'underscore' tested method/property name. Different words should be capitalized (and optionally separated by 'underscore').

Right:

export function test_goToVisualState_NoState_ShouldResetStyledProperties() {
    // Test code here.
}