TypeScript Functions All In One

TypeScript Functions All In One

demos

type Log = (a: any) => void;

const log: Log = console.log;

log(`typescript function`);

.d.ts

type Log = (a: any) => void;
declare const log: Log;

https://www.typescriptlang.org/play?#code/C4TwDgpgBAMg9gcygXigCgIYC4oYHYgCUKAfFAG5wCWAJgNwCwAUMwMZx4DOwUANojnhJU7LnF4QAdPwSMWTGWgAGoSJ1YAnKmB4AzAK55WwKhyWE5QA

// function type & type alias
type Log = (...data: any[]) => void;

const log: Log = console.log;

log(`typescript function`);

Node.js & console.log

https://github.com/nodejs/node/blob/v16.4.2/lib/console.js

https://github.com/nodejs/node/blob/v16.4.2/lib/internal/console/global.js

https://github.com/nodejs/node/blob/v16.4.2/lib/internal/console/constructor.js

(method) Console.log(...data: any[]): void (+1 overload)

namespace console
var console: Console
The console module provides a simple debugging console that is similar to the JavaScript console mechanism provided by web browsers.

The module exports two specific components:

A Console class with methods such as console.log(), console.error() andconsole.warn() that can be used to write to any Node.js stream.
A global console instance configured to write to process.stdout and process.stderr. The global console can be used without callingrequire('console').
Warning: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the note on process I/O for more information.

Example using the global console:

console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints error message and stack trace to stderr:
//   Error: Whoops, something bad happened
//     at [eval]:5:15
//     at Script.runInThisContext (node:vm:132:18)
//     at Object.runInThisContext (node:vm:309:38)
//     at node:internal/process/execution:77:19
//     at [eval]-wrapper:6:22
//     at evalScript (node:internal/process/execution:76:60)
//     at node:internal/main/eval_string:23:3

const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console class:

const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);

myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err

const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
@see — source

Function Type

1. function type expression / 函数类型表达式

// 显式的声明 ts function 返回值 void
function greeter(fn: (a: string) => void): void {
  fn("Hello, World");
}

function printToConsole(s: string): void {
  console.log(s);
}

greeter(printToConsole);
// function printToConsole(s: string): void
// function greeter(fn: (a: string) => void): void

// ts function  默认返回值 void
function greeter(fn: (a: string) => void) {
  fn("Hello, World");
}

function printToConsole(s: string) {
  console.log(s);
}

greeter(printToConsole);
// function printToConsole(s: string): void
// function greeter(fn: (a: string) => void): void

declare function greeter(fn: (a: string) => void): void;
declare function printToConsole(s: string): void;

function greeter1(fn: (a: string) => void) {
  fn("Hello, World");
  // 自动类型推断 number
  return 1;
}
// declare function greeter(fn: (a: string) => void): number;

// 显式的声明 ts function 返回值 any
function greeter2(fn: (a: string) => void): any {
  fn("Hello, World");
  return 2;
}
// declare function greeter2(fn: (a: string) => void): any;

type alias / 类型别名

// type GreetFunction = (a) => void;
// 不声明，默认的参数类型是 any
// type GreetFunction = (a: any) => void;

// 类型别名
type GreetFunction = (a: string) => void;

function greeter(fn: GreetFunction) {
   fn("Hello, World");
}

2. Call Signatures / 调用签名

type DescribableFunction = {
  description: string;
  (arg: string): any;
};

function greeter(fn: DescribableFunction) {
  console.log(`fn.description`, fn.description);
  fn("Hello, World");
  return 2;
}

function func(s: string): void {
  console.log(`s =`, s);
}

// function is Object
func.description = 'xyz';

greeter(func);

type DescribableFunction = {
    description: string;
    (arg: string): any;
};
declare function greeter(fn: DescribableFunction): number;
declare function func(s: string): void;
declare namespace func {
    var description: string;
}

TypeScript

Functions

https://www.typescriptlang.org/docs/handbook/functions.html

More on Functions

https://www.typescriptlang.org/docs/handbook/2/functions.html

refs

https://github.com/xgqfrms/learn-typescript-by-practice

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