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JavaScript

Ben Os
Ben Os
20,008 Points
Posted by Ben Os
Ben Os
20,008 Points

NodeJS --- SyntaxError: Unexpected token N in JSON at position 0 (a bug in the console)?

As this lesson I used the following code to execute my program with node app.js chalkers alenaholligan in the terminal.

Yet I get:

NodeJS --- SyntaxError: Unexpected token N in JSON at position 0

Here the code I used. I looked again and again and also used a debugger but I couldn't fin any syntax error:

function printMessage(username, badges, points) {
    let message = `${username} has ${badges} total badge(s) and ${points} points in Javascript.`;
    console.log(message);
}

// printMessage('chalkers', 100, 2000000);

let https = require('https');
function getProfile(username) {

    let request = https.get(`https://teamtreehouse.com/${username}.json`, (response)=> {
        let responseBody = '';

        response.on("data", (dataChunk)=> {
          responseBody += dataChunk.toString();
        });

        response.on("end", ()=> {
            let profile = JSON.parse(responseBody);
            printMessage(username, profile.badges.length, profile.points.JavaScript);
        });

        request.on("error", (error)=> {
            console.error(error.message);
        });
    });
}

    let users = process.argv.slice(1); // cut one of the 3.
    users.forEach(getProfile);

Why won't it work? Might it be a bug in the console?

Andrew Chalkley Dave McFarland

2 Answers

Alexander La Bianca
Alexander La Bianca
15,959 Points

All slice(2) does is get rid of the two items in argv that are not usernames. Those are the ones you saw when you logged the argv value. After you start entering values in the console, your argv will contain the values you entered. The slice method does have nothing to do with how many usernames you entered. It is very common actually in node to do the argv.slice(2) as the first two items are not used in most console node based applications.

So when you start before you pass in anything. Your argv will always be:

//argv
[ '/usr/local/nodejs-binary-6.11.1/bin/node', '/home/treehouse/workspace/app.js' ]

//argv[0] is '/usr/local/nodejs-binary-6.11.1/bin/node'

//argv[1] is '/home/treehouse/workspace/app.js'

Then you start entering usernames so after you enter the first username the argv value is

//argv
[ '/usr/local/nodejs-binary-6.11.1/bin/node', '/home/treehouse/workspace/app.js', 'chalkers' ]

Now when you do your slicing with 1 instead of 2 you are assigning a non username into your users array

let users = process.argv.slice(1)
//now users is:   ['/home/treehouse/workspace/app.js', 'chalkers']

Now you are doing your forEach loop with that users array. Well the first item in the users array is clearly not a username that is on treehouse. So treehouse will give you back 'Not Found' which is not valid JSON. That's why you get the error

But if you do slicing with 2 you will only grab anything in the argv array that is AFTER the first two items

let users = process.argv.slice(2)
//now users is: ['chalkers']

Now you only have valid usernames.

Check our the Array.slice() method on MDN for clarity. https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/slice

Ben Os
Ben Os
20,008 Points
Ben Os
Ben Os
20,008 Points

Thanks, I now understood that.

Alexander La Bianca
Alexander La Bianca
15,959 Points
Alexander La Bianca
Alexander La Bianca
15,959 Points

The issue is your line:

let users = process.argv.slice(1);

//Needs to change to
let users = process.argv.slice(2);

You got the error because you also searched for a username of the value at argv[1] which is the path of the file that is running the node.js program. Which is why the teamtreehouse api returned NOT FOUND which is invalid JSON. I see you had the exact same error because it states:

NodeJS --- SyntaxError: Unexpected token N in JSON at position 0 N is the N of the NOT FOUND

console log the process.argv value and you see what I mean

Ben Os
Ben Os
20,008 Points
Ben Os
Ben Os
20,008 Points

Sadly your answer isn't clear to me. When I print process.argv with console.log I get the following stdout in execution:

[ '/usr/local/nodejs-binary-6.11.1/bin/node', '/home/treehouse/workspace/app.js' ]

In slice I wrote 1 instead of 2 because I gave only two usernames instead of three (as in Chalk's original example). I did so by means of minimalism --- To bring one of the two with slice, but not the two, as in:

node app.js chalkers alenaholligan

And yet id I change the slice() integer to 2 (even if I pass 2 names or three names), it works.

So, I still miss why the integer passed to slice() make any difference. I mean, I still miss why 1 won't work but 2 will.