Go与JavaScript中方法的执行上下文

下面是两个代码片段——一个在Go中，另一个在JavaScript中——基本上做着相同的事情

//开始

package main    

import "fmt"

type Engine struct {
  bootTimeInSecs int
}

func (e *Engine) Start() {
  fmt.Printf("Engine starting in %s seconds ...", e.bootTimeInSecs)
}

type Start func() 

type BenchmarkSuite struct {
  workloads []string
  start Start 
}

func main() {
  engine := Engine{10}
  benchmarkSuite := BenchmarkSuite{workloads: []string{}, start: engine.Start}
  benchmarkSuite.start()
}

输出

Engine starting in 10 seconds ...

function Engine(bootTimeInSecs) {
    this.bootTimeInSecs = bootTimeInSecs
}

Engine.prototype.constructor = Engine
Engine.prototype.Start = function() {
  console.log("Engine starting in " + this.bootTimeInSecs + " seconds ...")
}

function BenchmarkSuite(workloads, start) {
    this.workloads = workloads
    this.start = start
} 

BenchmarkSuite.prototype.constructor = BenchmarkSuite

engine = new Engine(10)
benchmarkSuite = new BenchmarkSuite([], engine.Start)
benchmarkSuite.start()

Engine starting in undefined seconds ...

//JavaScript

Engine starting in 10 seconds ...

function Engine(bootTimeInSecs) {
    this.bootTimeInSecs = bootTimeInSecs
}

Engine.prototype.constructor = Engine
Engine.prototype.Start = function() {
  console.log("Engine starting in " + this.bootTimeInSecs + " seconds ...")
}

function BenchmarkSuite(workloads, start) {
    this.workloads = workloads
    this.start = start
} 

BenchmarkSuite.prototype.constructor = BenchmarkSuite

engine = new Engine(10)
benchmarkSuite = new BenchmarkSuite([], engine.Start)
benchmarkSuite.start()

Engine starting in undefined seconds ...

输出

Engine starting in 10 seconds ...

function Engine(bootTimeInSecs) {
    this.bootTimeInSecs = bootTimeInSecs
}

Engine.prototype.constructor = Engine
Engine.prototype.Start = function() {
  console.log("Engine starting in " + this.bootTimeInSecs + " seconds ...")
}

function BenchmarkSuite(workloads, start) {
    this.workloads = workloads
    this.start = start
} 

BenchmarkSuite.prototype.constructor = BenchmarkSuite

engine = new Engine(10)
benchmarkSuite = new BenchmarkSuite([], engine.Start)
benchmarkSuite.start()

Engine starting in undefined seconds ...

---

我知道JavaScript的解决方法，但这不是问题所在。为什么JavaScript决定不保留函数的原始执行上下文？

在JavaScript中，当您将对象传递给

基准测试套件

构造函数时，函数未绑定到对象

引擎

必须将对象显式绑定到函数。 这就是你必须要做的

benchmarkSuite = new BenchmarkSuite([], engine.Start.bind(engine))

bind（）最简单的用法是生成一个函数，该函数无论如何调用，都是使用特定的this值调用的。对于新的JavaScript程序员来说，一个常见的错误是从对象中提取一个方法，然后调用该函数，并期望它使用原始对象作为它的this（例如，在基于回调的代码中使用该方法）。然而，如果不特别小心，原始对象通常会丢失。使用原始对象从函数创建绑定函数，巧妙地解决了这个问题

你可以参考更多

函数引擎（boottimenses）{
this.boottimenses=boottimenses
}
Engine.prototype.constructor=引擎
Engine.prototype.Start=函数（）{
console.log（“引擎在“+this.boottimenses+”秒内启动…”）
}
功能基准测试套件（工作负载、启动）{
this.workloads=工作负载
this.start=开始
} 
BenchmarkSuite.prototype.constructor=BenchmarkSuite
发动机=新发动机（10）
benchmarkSuite=新的benchmarkSuite（[]，engine.Start.bind（engine））
benchmarkSuite.start（）

无论是谁对该问题进行了

结束

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