问如何在D3.js中使用大型Json文件

EN

var fs = require('fs');

// open the file
fs.readFile('./foods-2011-10-03.json','utf8',function(err,data){
    if (err) throw err;
    var output = [];

    // parse the file from a string into an object
    data = JSON.parse(data);

    // Loop through each element
    data.forEach(function(d,i){
        // spit an example element into the console for inspection:
        // if ( i == 0 ) console.log(d);

        // decide which parts of the object you'd like to keep
        var element = {
            description : d.description,
            nutrients : []
        };

        // for example here I'm just keeping vitamins
        d.nutrients.forEach(function(d,i){
            if ( d.description.indexOf("Vitamin") == 0 ) element.nutrients.push(d);
        });

        output.push(element);
    })

    fs.writeFile( './foods-output.json', JSON.stringify(output), function(err){
        if ( err ) throw err;
        console.log('ok');
    })
})