go 执行js代码引擎系列之三：v8go库

写在前面

本文是《go执行js代码引擎系列》文章之第一篇，其他相关文章如下

• go执行js代码引擎系列之一：goja库
• go执行js代码引擎系列之二：otto库
• go执行js代码引擎系列总结篇：比较goja、otto、v8go

v8go

基本用法

package main

import (
   "fmt"
   v8 "rogchap.com/v8go"
)

func main() {
   ctx := v8.NewContext()                                  // creates a new V8 context with a new Isolate aka VM
   ctx.RunScript("const add = (a, b) => a + b", "math.js") // executes a script on the global context
   ctx.RunScript("const result = add(3, 4)", "main.js")    // any functions previously added to the context can be called
   val, _ := ctx.RunScript("result", "value.js")           // return a value in JavaScript back to Go
   fmt.Printf("addition result: %s", val)
}

输出：addition result: 7

One VM, many contexts

iso := v8.NewIsolate() // creates a new JavaScript VM
ctx1 := v8.NewContext(iso) // new context within the VM
ctx1.RunScript("const multiply = (a, b) => a * b", "math.js")

ctx2 := v8.NewContext(iso) // another context on the same VM
if _, err := ctx2.RunScript("multiply(3, 4)", "main.js"); err != nil {
  // this will error as multiply is not defined in this context
}

不同的ctx之间是隔离的，ctx可以继承

设置go function的回调函数

iso := v8.NewIsolate() // create a new VM
// a template that represents a JS function
printfn := v8.NewFunctionTemplate(iso, func(info *v8.FunctionCallbackInfo) *v8.Value {
    fmt.Printf("%v", info.Args()) // when the JS function is called this Go callback will execute
    return nil // you can return a value back to the JS caller if required
})
global := v8.NewObjectTemplate(iso) // a template that represents a JS Object
global.Set("print", printfn) // sets the "print" property of the Object to our function
ctx := v8.NewContext(iso, global) // new Context with the global Object set to our object template
ctx.RunScript("print('foo')", "print.js") // will execute the Go callback with a single argunent 'foo'

js错误

val, err := ctx.RunScript(src, filename)
if err != nil {
  e := err.(*v8.JSError) // JavaScript errors will be returned as the JSError struct
  fmt.Println(e.Message) // the message of the exception thrown
  fmt.Println(e.Location) // the filename, line number and the column where the error occured
  fmt.Println(e.StackTrace) // the full stack trace of the error, if available

  fmt.Printf("javascript error: %v", e) // will format the standard error message
  fmt.Printf("javascript stack trace: %+v", e) // will format the full error stack trace
}

js打样堆栈

func createProfile() {
	iso := v8.NewIsolate()
	ctx := v8.NewContext(iso)
	cpuProfiler := v8.NewCPUProfiler(iso)

	cpuProfiler.StartProfiling("my-profile")

	ctx.RunScript(profileScript, "script.js") # this script is defined in cpuprofiler_test.go
	val, _ := ctx.Global().Get("start")
	fn, _ := val.AsFunction()
	fn.Call(ctx.Global())

	cpuProfile := cpuProfiler.StopProfiling("my-profile")

	printTree("", cpuProfile.GetTopDownRoot()) # helper function to print the profile
}

func printTree(nest string, node *v8.CPUProfileNode) {
	fmt.Printf("%s%s %s:%d:%d\n", nest, node.GetFunctionName(), node.GetScriptResourceName(), node.GetLineNumber(), node.GetColumnNumber())
	count := node.GetChildrenCount()
	if count == 0 {
		return
	}
	nest = fmt.Sprintf("%s  ", nest)
	for i := 0; i < count; i++ {
		printTree(nest, node.GetChild(i))
	}
}

// Output
// (root) :0:0
//   (program) :0:0
//   start script.js:23:15
//     foo script.js:15:13
//       delay script.js:12:15
//         loop script.js:1:14
//       bar script.js:13:13
//         delay script.js:12:15
//           loop script.js:1:14
//       baz script.js:14:13
//         delay script.js:12:15
//           loop script.js:1:14
//   (garbage collector) :0:0

但是需要手动开启、停止cpuPrifile