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POParse large JSON file in Nodejs
 

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    <p>I have a file which stores many JavaScript objects in JSON form and I need to read the file, create each of the objects, and do something with them (insert them into a db in my case). The JavaScript objects can be represented a format:</p> <p><strong>Format A:</strong></p> <pre><code>[{name: 'thing1'}, .... {name: 'thing999999999'}] </code></pre> <p>or <strong>Format B:</strong></p> <pre><code>{name: 'thing1'} // &lt;== My choice. ... {name: 'thing999999999'} </code></pre> <p>Note that the <code>...</code> indicates a lot of JSON objects. I am aware I could read the entire file into memory and then use <code>JSON.parse()</code> like this:</p> <pre><code>fs.readFile(filePath, 'utf-8', function (err, fileContents) { if (err) throw err; console.log(JSON.parse(fileContents)); }); </code></pre> <p>However, the file could be really large, I would prefer to use a stream to accomplish this. The problem I see with a stream is that the file contents could be broken into data chunks at any point, so how can I use <code>JSON.parse()</code> on such objects? </p> <p>Ideally, each object would be read as a separate data chunk, but I am not sure on <em>how to do that</em>.</p> <pre><code>var importStream = fs.createReadStream(filePath, {flags: 'r', encoding: 'utf-8'}); importStream.on('data', function(chunk) { var pleaseBeAJSObject = JSON.parse(chunk); // insert pleaseBeAJSObject in a database }); importStream.on('end', function(item) { console.log("Woot, imported objects into the database!"); });*/ </code></pre> <p>Note, I wish to prevent reading the entire file into memory. Time efficiency does not matter to me. Yes, I could try to read a number of objects at once and insert them all at once, but that's a performance tweak - I need a way that is guaranteed not to cause a memory overload, not matter how many objects are contained in the file. </p> <p>I can choose to use <code>FormatA</code> or <code>FormatB</code> or maybe something else, just please specify in your answer. Thanks!</p>
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    1. COFor format B you could parse through the chunk for new lines, and extract each whole line, concatenating the rest if it cuts off in the middle. There may be a more elegant way though. I haven't worked with streams to much.
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