Javascript 无法推送到函数内部的全局数组

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我有一个文件夹，里面装满了 json 文件，我正试图将它们全部推送到一个数组中。但是，外部数组是空白的。任何关于为什么会发生这种情况或解释更好方法的帮助将不胜感激。

var fs = require('fs');
var dataFolder = './jsonData/';

var arr = [];
fs.readdir(dataFolder, (err, files) => {
    files.forEach(file => {
        fs.readFile(dataFolder + file, 'utf8', function (err, data) {
            if (err) throw err;
            arr.push(data);
            console.log (arr); // correct output
        })
    })
})
console.log (arr);  //output is []

很抱歉它看起来很丑，但这是内部数组的一些输出:

[ '{\n "title": "A New Kind of Science [Hardcover]",\n "author": "Stephen Wolfram",\n "price": "$20.73",\n "shippingWeight": "5.6 磅",\n "isbn10": "1579550088"\n}' ]

[ '{\n "title": "A New Kind of Science [Hardcover]",\n "author": "Stephen Wolfram",\n "price": "$20.73",\n "shippingWeight": "5.6 磅",\n "isbn10": "1579550088"\n}', '{\n "title": "I Wear the Black Hat: Grapping with Villains (Real and Imagined) [Hardcover]",\n "author": "Chuck Klosterman",\n "price": "$15.49",\n "shippingWeight": "2.2 磅",\n "isbn10": "1439184496"\n}' ]

最佳答案

readdir 是异步的，它在您到达 console.log 时尚未执行。