判斷l(xiāng)oader返回值是否為promise，是就等待promise完成，得到值，否則直接獲取返回值。

async function useLoader(source, loaders = []) {
	//...省略loader過(guò)濾階段,假設(shè)loaderList = loaders
    
    const loaderList = loaders

    async function runLoader(source, loaderList) {
        const loader = loaderList.pop()
        let newSource
        if (isPromise(loader)) newSource = await loader(source)
        else newSource = loader(source)
        if (loaderList.length > 0) return runLoader(newSource, loaderList)
        else return newSource

    }

    source = await runLoader(source, loaderList)

    return source
}
復(fù)制代碼

使用await等待異步loader返回結(jié)果。這里有個(gè)問(wèn)題，假如使用Array.prototype上的foreach方法，是一個(gè)同步方法，無(wú)法提供一個(gè)可由外部控制的異步環(huán)境，將傳入的callback進(jìn)行堵塞，因此此處采用了for-of進(jìn)行循環(huán)。

async function analyzeFileToLoard(inputPath, outputPath) {
    let source = readFile(inputPath)
    const loaders = config.module
    for (let loader of loaders) {
        if (loader.test.test(inputPath)) {
            source = await useLoader(source, loader.loader, outputPath)
            if (loader.outputPath) outputPath = loader.outputPath(outputPath)
        }
    }

    writeFile(outputAppPath(outputPath), source)
}
復(fù)制代碼

可以用之前foreach的習(xí)慣調(diào)用。

Array.prototype.asyncForeach = async function(callBack) {
    if (callBack.constructor.name !== 'AsyncFunction') throw new Error('callBack should be AsyncFunction!')
    for (let i = 0; i<this.length; i ++ ) {
        const item = this[i]
        await callBack(item, i)
    }
}

// 調(diào)用
async function analyzeFileToLoard(inputPath, outputPath) {
    let source = readFile(inputPath)
    const loaders = config.module

    await loaders.asyncForeach(async loader => {
        if (loader.test.test(inputPath)) {
            const res = await useLoader(source, loader.loader, outputPath)
            source = res
            if (loader.outputPath) outputPath = loader.outputPath(outputPath)
        }
    })
    writeFile(outputAppPath(outputPath), source)
}