node-13.x API
scarcoco opened this issue · comments
node.org document
Usage
http://nodejs.org/dist/latest-v13.x/docs/api/events.html
import { EventEmitter } from 'events'
const emitter = new EventEmitter()
emitter.on('error', (err) => {
console.log(err)
})
emitter.on('one', (...args) => {
console.log('on event -> one(1): ', args)
})
emitter.on('one', (...args) => {
console.log('on event -> one(2): ', args)
})
// once
emitter.once('two', (...args) => {
console.log('once event -> two: ', args)
})
emitter.emit('one', 1, 2)
emitter.emit('one', 3, 4)
emitter.emit('two', 5, 6)
emitter.emit('two', 7, 8)Buffer
今天终于认真的把 Buffer 的文档认真看了一下，大致梳理一下。
Buffer和 字符编码
支持的字符编码方式有 utf8、utf16le、latin1，把 Buffer 转变为上诉编码称为解码，反之称为编码。
Node 也支持 hex 和 base64 两种二进制和字符串互转编码，对于二进制和字符串互转，把 Buffer 转为字符串称为编码，反之称为解码。
另外还有三种遗留的编码方式：ascii、binary（latin1）、ucs2（utf16le）。
Buffer和TypedArray的关系；
Buffer 实例也是 Uint8Array 实例，Uint8Array 是 TypedArray 的子类，所以 TypedArray 的方法 Buffer 也有，除了：
TypedArray#slice()create a copy of TypedArray，butBuffer#slice()only create a view over original Buffer；TypedArray#subarray()的效果和Buffer#slice效果一致；buffer.toString()和它对应的TypedArray的toString不兼容；indexOf等方法支持更多参数；
Buffer 和 TypedArray 互转时，直接使用则会拷贝元素，为了复用内存，可以使用 ArrayBuffer 属性。
When passing a Buffer to a TypedArray constructor, the Buffer’s elements will be copied, interpreted as an array of integers, and not as a byte array of the target type.
In order to create a TypedArray that shares its memory with the Buffer, the underlying ArrayBuffer can be passed to the TypedArray constructor instead:
const buf = Buffer.from('hello', 'utf16le');
const uint16arr = new Uint16Array(
buf.buffer, buf.byteOffset, buf.length / Uint16Array.BYTES_PER_ELEMENT);
It is also possible to create a new Buffer that shares the same allocated memory as a TypedArray instance by using the TypedArray object’s .buffer property in the same way
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
it is possible to use only a portion of the underlying ArrayBuffer by passing in byteOffset and length parameters:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
TypedArray & Buffer 差异如下：
TypedArray.from(source[, mapFn[, thisArg]])
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset[, length]])
Buffer.from(string[, encoding])
Buffer和iteration
支持 keys、values、entries 等方法
Buffer.from()、Buffer.alloc()、Buffer.allocUnsafe()、Buffer.allocUnsafeSlow()、Buffer.poolSize、new Buffer()、new SlowBuffer(size)、node --zero-fill-buffers关系
new Buffer()和new SlowBuffer(size)已经废弃，具体可以查看文档。Buffer.from()用法如上；Buffer.alloc()、Buffer.allocUnsafe()、Buffer.allocUnsafeSlow()、Buffer.poolSize
Buffer.allocUnsafe()
The Buffer module pre-allocates an internal Buffer instance of size Buffer.poolSize that is used as a pool for the fast allocation of new Buffer instances created using Buffer.allocUnsafe() and the deprecated new Buffer(size) constructor only when size is less than or equal to Buffer.poolSize >> 1 (floor of Buffer.poolSize divided by two).
Buffer.allocUnsafeSlow()
However, in the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled Buffer instance using Buffer.allocUnsafeSlow() and then copying out the relevant bits
Buffer
今天终于认真的把 Buffer 的文档认真看了一下，大致梳理一下。
Buffer和 字符编码
支持的字符编码方式有 utf8、utf16le、latin1，把 Buffer 转变为上诉编码称为解码，反之称为编码。
Node 也支持 hex 和 base64 两种二进制和字符串互转编码，对于二进制和字符串互转，把 Buffer 转为字符串称为编码，反之称为解码。
另外还有三种遗留的编码方式：ascii、binary（latin1）、ucs2（utf16le）。
Buffer和TypedArray的关系；
Buffer 实例也是 Uint8Array 实例，Uint8Array 是 TypedArray 的子类，所以 TypedArray 的方法 Buffer 也有，除了：
TypedArray#slice()create a copy of TypedArray，butBuffer#slice()only create a view over original Buffer；TypedArray#subarray()的效果和Buffer#slice效果一致；buffer.toString()和它对应的TypedArray的toString不兼容；indexOf等方法支持更多参数；
Buffer 和 TypedArray 互转时，直接使用则会拷贝元素，为了复用内存，可以使用 ArrayBuffer 属性。
When passing a Buffer to a TypedArray constructor, the Buffer’s elements will be copied, interpreted as an array of integers, and not as a byte array of the target type.
In order to create a TypedArray that shares its memory with the Buffer, the underlying ArrayBuffer can be passed to the TypedArray constructor instead:
const buf = Buffer.from('hello', 'utf16le');
const uint16arr = new Uint16Array(
buf.buffer, buf.byteOffset, buf.length / Uint16Array.BYTES_PER_ELEMENT);
It is also possible to create a new Buffer that shares the same allocated memory as a TypedArray instance by using the TypedArray object’s .buffer property in the same way
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`.
const buf1 = Buffer.from(arr);
// Shares memory with `arr`.
const buf2 = Buffer.from(arr.buffer);
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 a0 0f>
arr[1] = 6000;
console.log(buf1);
// Prints: <Buffer 88 a0>
console.log(buf2);
// Prints: <Buffer 88 13 70 17>
it is possible to use only a portion of the underlying ArrayBuffer by passing in byteOffset and length parameters:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
console.log(buf.length);
TypedArray & Buffer 差异如下：
TypedArray.from(source[, mapFn[, thisArg]])
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset[, length]])
Buffer.from(string[, encoding])
Buffer和iteration
支持 keys、values、entries 等方法
Buffer.from()、Buffer.alloc()、Buffer.allocUnsafe()、Buffer.allocUnsafeSlow()、Buffer.poolSize、new Buffer()、new SlowBuffer(size)、node --zero-fill-buffers关系
new Buffer()和new SlowBuffer(size)已经废弃；Buffer.from()用法如上；Buffer.alloc()、Buffer.allocUnsafe()、Buffer.allocUnsafeSlow()、Buffer.poolSize
Buffer.allocUnsafe()
The Buffer module pre-allocates an internal Buffer instance of size Buffer.poolSize that is used as a pool for the fast allocation of new Buffer instances created using Buffer.allocUnsafe() and the deprecated new Buffer(size) constructor only when size is less than or equal to Buffer.poolSize >> 1 (floor of Buffer.poolSize divided by two).
Buffer.allocUnsafeSlow()
However, in the case where a developer may need to retain a small chunk of memory from a pool for an indeterminate amount of time, it may be appropriate to create an un-pooled Buffer instance using Buffer.allocUnsafeSlow() and then copying out the relevant bits